Endocervical-like mucinous borderline tumors of the ovary: a clinicopathologic analysis of 31 cases

The diverse morphology and immunophenotype of ovarian endometrioid carcinomas

Endometrioid carcinoma (EC) accounts for approximately 10-12% of ovarian epithelial malignancies but compared to its relative frequency, results in a disproportionate number of diagnostically difficult cases with potential for misdiagnosis. In this review the protean and diverse morphologies of ovarian EC are discussed, including 'metaplastic' changes, EC with spindle cell differentiation/corded and hyalinised features and EC with sex cord-like formations. The propensity for 'transdifferentiation' in ovarian ECs is also discussed, one example being the association with a somatically derived yolk sac tumour. Although immunohistochemistry may be extremely useful in diagnosing EC and in distinguishing between EC and other ovarian epithelial malignancies, metastatic neoplasms and sex cord-stromal tumours, this review also discusses the propensity for ovarian EC to exhibit an aberrant immunophenotype which may compound diagnostic uncertainty. The genomic characteristics of these tumours and the recent 'incorporation' of seromucinous carcinoma into the EC category are also discussed.

Clinicopathologic Features and the Loss of ARID1A Expression in Ovarian Seromucinous Borderline Tumors and Seromucinous Carcinomas

The current study highlighted the ARID1A and SALL4 expression and described histopathologic and immunohistochemical features of ovarian seromucinous tumors (SMTs) including borderline tumors (SMBTs) and seromucinous carcinomas (SMC; namely as endometrioid carcinoma with mucinous differentiation according to WHO 2020 classification). The clinicopathological and immunohistochemical features of 38 SMTs were analyzed, including ARID1A, SALL4, estrogen receptor (ER), progesterone receptor (PR), TP53, keratin 7, keratin 20, CEA, CDX2, WT1, PAX2, and PAX8. SMCs and SMBTs comprised 68.4% (n = 26) and 31.6% (n = 12) of all SMTs, respectively, studied. The mean age of diagnosis was 47.4 years and 41.4 years, and the mean size was 9 cm and 7.45 cm for SMC and SMBT, respectively. There was endometriosis or endometriotic cyst in 61.5% of SMCs and 50% of SMBTs. Immunohistochemically, loss of ARID1A staining was observed in 15 (65.2%) of 26 SMCs, and 3 (33.3%) of the 12 SMBTs. Only one SMC showed focal SALL4 positivity. All SMTs were positive for ER, PR, PAX8, and keratin 7. SMTs were negative for WT1, keratin 20, CDX2, and CEA (negative in 66.7% to 92.3% of the cases). While all SMBTs and 24 (92.3%) of 26 SMCs exhibited “wild-type” TP53 staining, 2 (7.7%) SMCs, both were stage III, showed mutant type TP53 overexpression. We indicate there is a similarity between SMC and SMBT according to the immunohistochemical features. SMBTs are keratin 7, ER, PR positive tumors, and some of them have loss of ARID1A expression and are likely to develop in the background of endometriosis similar to SMC.

Oncological and reproductive outcomes after fertility-sparing surgery in patients with seromucinous borderline ovarian tumor: Results of a large retrospective study

OBJECTIVE

To evaluate the oncological and reproductive outcomes in patients with seromucinous borderline ovarian tumors (SMBOT) treated with fertility-sparing surgery (FSS).

METHODS

We retrospectively reviewed the medical records of patients with SMBOT who underwent surgery between 2000 and 2019. A centralized histological review was performed and recurrence rates were compared between different surgical procedures.

RESULTS

A total of 105 patients fulfilled the inclusion criteria, of whom 65 underwent FSS and 40 were treated with radical surgery (RS). Fourteen patients had recurrent disease after a median follow-up time of 59.6 months (range: 22.1-256.8 months). All but one relapsed with SMBOT. There was no significant difference in disease-free survival (DFS) between the two groups (P = 0.141). Multivariate analysis showed that only bilateral involvement was associated with increased recurrence (P = 0.008). In the subgroup of patients treated with conservative surgery, there was no significant difference in DFS with regard to surgical procedures (ovarian cystectomy vs salpingo-oophorectomy, P = 0.487). Of the 12 patients in the FSS group who developed recurrence, 11 underwent a second round of FSS and all remained alive with no evidence of disease at the end of follow-up. Of 20 patients desiring pregnancy, 16 patients were successful and resulted in 17 term deliveries.

CONCLUSIONS

FSS is feasible for young patients who wish to preserve their fertility. Patients initially treated with ovarian cystectomy may be managed by close surveillance if post-operative imaging are negative. Repeat FSS remains a valuable alternative for young patients with recurrent SMBOT after thorough communication.

Ovarian mucinous and seromucinous neoplasms: problematic aspects and modern diagnostic approach

The morphological spectrum of primary ovarian mucinous and seromucinous tumours is broad and presents an array of diagnostic challenges, many unique to these tumour types. This reflects the heterogeneous nature of these lesions, their varied histogenesis and evolving classification systems over recent decades, with further modification to the seromucinous category incorporated in the recently published 5^th edition of the WHO Classification of Female Genital Tumours. In this review we provide an update on the classification of these neoplasms and discuss their histogenesis and diverse morphology, focusing on areas which are diagnostically problematic. We also cover tumour grading, differential diagnosis, immunohistochemistry, the recent elucidation of the molecular underpinnings of ovarian mucinous neoplasia and discuss the gross and intraoperative handling of these tumours. A number of diagnostic issues remain unresolved highlighting the importance of further research on this front, as well as a multidisciplinary approach in the care of patients with ovarian mucinous and seromucinous neoplasia.

Ovarian Seromucinous Borderline Tumors Are Histologically Different from Mucinous Borderline Tumors

AIM

To examine the clinicopathological features of ovarian seromucinous borderline tumors (SMBTs) and compare them with those of mucinous borderline/atypical proliferative mucinous tumors (MB/APMTs).

PATIENTS AND METHODS

Patients with SMBT between 2014 and 2018 and those with MB/APMT between 1988 and 2018 who underwent surgery at our Institution were identified. Pathological review was conducted using the 2014 World Health Organization criteria. Clinical features were compared retrospectively between SMBT and MB/APMT.

RESULTS

In total, 11 (12.9%) patients with SMBT and 74 (87.1%) patients with MB/APMT were included in our study. The diagnosis of six patients with SMBT and 73 patients with MB/APMT was not revised on review. SMBT was diagnosed at a younger age (p=0.04), was of smaller size (p<0.01) and bilateral (p=0.03), coexisted with endometriosis (p<0.01), and more frequently recurred than MB/APMT (p=0.04).

CONCLUSION

SMBT might be more aggressive than MB/APMT.

Comprehensive genomic profiling reveals ubiquitous KRAS mutations and frequent PIK3CA mutations in ovarian seromucinous borderline tumor

The molecular underpinnings of seromucinous borderline tumor (SMBT) - an uncommon ovarian epithelial neoplasm characterized by association with endometriosis, frequent bilateral ovarian involvement, and occasional progression to invasive carcinoma - remain poorly understood. Here, we sought to comprehensively characterize the mutational landscape of SMBT and elucidate the clonal relationship between bilateral ovarian SMBTs. We also compared the mutational profiles between SMBTs and concurrent invasive carcinomas. Formalin-fixed, paraffin-embedded tissue specimens were retrieved from 28 patients diagnosed with SMBT. Massively parallel sequencing of 409 cancer-related genes was conducted to identify somatic mutations in 33 SMBT samples and four concurrent invasive carcinoma specimens. TERT promoter mutations were assessed by Sanger sequencing, whereas immunohistochemistry was used as a surrogate tool for detecting deletions or epigenetic silencing of relevant tumor suppressor genes. Twenty-six (92.9%) of the 28 patients were diagnosed with stage I SMBTs. Seven (25%) cases showed bilateral ovarian involvement and 13 (46%) had concomitant endometriosis. Concurrent ovarian carcinomas were identified in three patients, whereas one case had a synchronous endometrial carcinoma. Somatic mutations in the KRAS, PIK3CA, and ARID1A genes were identified in 100, 60.7, and 14.3% of SMBT samples, respectively. In contrast, TERT promoter mutations and DNA mismatch repair deficiencies were absent. Sequencing of paired specimens from patients with bilateral SMBT revealed the presence of at least two shared somatic mutations, suggestive of a clonal relationship. Similarly, we identified shared somatic mutations between SMBT samples and concurrent ovarian carcinoma specimens. Taken together, these findings demonstrated a distinct mutational landscape of SMBT in which (1) KRAS is invariably mutated, (2) PIK3CA is frequently mutated, and (3) TERT promoter mutations and DNA mismatch repair deficiencies are absent. Our findings represent the first extensive characterization of this rare ovarian neoplasm, with potential implications for disease classification and molecular diagnostics.

Ovarian seromucinous cystadenomas and adenofibromas: first report of a case series

AIMS

To report a series of benign ovarian seromucinous neoplasms, an uncommon and hitherto poorly described category of tumours included in the current 2014 World Health Organisation classification of tumours of the female reproductive organs.

METHODS AND RESULTS

We report the clinicopathological features of a series of 22 benign ovarian seromucinous neoplasms (cystadenomas and adenofibromas or admixtures). The neoplasms occurred in patients aged 32-83 years (mean = 62, median = 65.5) and involved the left ovary (n = 14), the right ovary (n = 6) or both ovaries (n = 2). There was a common association with endometrioid elements (endometrioid differentiation within the cystadenoma/adenofibroma and/or endometriosis) and other endometriosis-associated neoplasms.

CONCLUSIONS

We speculate that some of these represent benign ovarian endometrioid neoplasms with foci of mucinous and/or serous differentiation, while others represent true mixed neoplasms.

[Borderline ovarian tumours: CNGOF Guidelines for clinical practice - Biopathology of ovarian borderline tumors]

OBJECTIVES

Ovarian borderline tumors (OBT) represent a heterogeneous group of lesions with specific management for each histological subtype. Thus, the correct histological diagnosis is mandatory.

MATERIAL AND METHODS

References were searched by PubMed from January 2000 to January 2018 and original articles in French and English literature were selected.

RESULTS AND CONCLUSIONS

OBT should be classified according to the last WHO classification. Any micro-invasion (foci<5mm) or microcarcinoma (foci<5mm with nuclear atypia and desmoplastic stromal reaction) should be indicated in the pathology report. In case of serous OBT, variants (classical or the micropapillary/cribriform) should be indicated (grade C). The peritoneal implants associated with OBT, should be classified as invasive or noninvasive, according to the extension into the underlying adipous tissue. If no adipous tissue is seen the term undetermined should be used (grade B). In case of mucinous OBT bilateral and/or with peritoneal implants or peritoneal pseudomyxoma a search for primitive gastrointestinal, appendiceal or biliopancreatic tumor should be performed (grade C). In case of OBT, a thorough sampling of the tumor is recommended, with 1 block/cm and 2 blocks/cm in case of mucinous OBT, serous OBT micropapillary variant, OBT with intraepithelial carcinoma or/and micro-invasion. Peritoneal implants should be examined in toto. Omentum without macroscopic lesion should be sampled in 4 to 6 blocks (grade C). In case of ovarian cyst suspicious for OBT, fine needle aspiration is not recommended (grade C). In case of ovarian tumor suspicious for OBT, intraoperative examination should be performed by a gynecological pathologist (grade C).

Endometriosis-related pathology: a discussion of selected uncommon benign, premalignant and malignant lesions

Endometriosis is an extremely common condition and, in most cases, establishing a histological diagnosis is straightforward, although a variety of benign alterations may result in problems with interpretation. In this review, I discuss selected uncommon variants of endometriosis or benign alterations that may result in diagnostic problems. The topics covered include the contentious issue of so-called atypical endometriosis, stromal endometriosis, polypoid endometriosis, and the association of endometriosis with florid mesothelial hyperplasia. The propensity of endometriosis to undergo neoplastic transformation (especially to endometrioid and clear cell carcinoma) is well known. Selected issues relating to the various neoplasms that can arise in endometriosis are discussed, with a particular concentration on unusual variants of endometrioid carcinoma that result in a disproportionately high number of issues in referral practice. The propensity of ovarian endometrioid carcinomas to show an unexpected ('aberrant') immunophenotype with positive staining with 'intestinal' markers and negative staining with Mullerian markers is also discussed. Uncommon tumour types that may arise in endometriosis, namely seromucinous neoplasms, mesonephric-like carcinomas, and somatically derived yolk sac tumours, are also covered.

MR findings for differentiating decidualized endometriomas from seromucinous borderline tumors of the ovary

PURPOSE

Decidualized endometriomas (DEs) and seromucinous borderline tumors (SMBTs) exhibit similar MR findings including markedly hyperintense mural nodules within endometriotic cysts on T2-weighted images. The present study aimed to assess the efficacy of MR imaging for differentiating between DEs and SMBTs of the ovary.

MATERIALS AND METHODS

MR images of 8 DEs and 14 SMBTs were retrospectively assessed and compared according to pathologies.

RESULTS

With regard to quantitative assessments of mural nodules, the number and signal intensity ratios (SIRs) on T1-weighted images were significantly greater in DEs than in SMBTs (11.0 ± 8.4 vs. 4.3 ± 4.1, p < 0.05 and 2.36 ± 0.56 vs. 1.49 ± 0.27, p < 0.01, respectively), whereas the height was significantly lower in DEs than in SMBTs (4.5 ± 1.4 mm vs. 21.9 ± 11.4 mm, p < 0.01). However, there were no significant differences between DEs and SMBTs in the SIRs on T2-weighted images, SIRs on diffusion-weighted images, and apparent diffusion coefficient values. With regard to qualitative assessments of mural nodules, the lobulated margin, pedunculated configuration, and T2 hypointense core were significantly more frequent in SMBTs than in DEs (71% vs. 0%, p < 0.01; 86% vs. 0%, p < 0.01; and 43% vs. 0%, p < 0.05, respectively).

CONCLUSION

The number, height, SIRs on T1-weighted images, lobulated margin, pedunculated configuration, and T2 hypointense core of mural nodules within endometriotic cysts were useful MR findings for differentiating DEs from SMBTs.

Ovarian Seromucinous Tumors: Pathogenesis, Morphologic Spectrum, and Clinical Issues

Ovarian seromucinous tumors were introduced in the 2014 World Health Organization (WHO) classification as one of the seven types of ovarian epithelial tumors. They are characterized by frequent association with endometriosis and bilaterality, microscopic appearance of papillary architecture, and admixture of a variety of müllerian-type epithelium. They are considered to be endometriosis-related ovarian neoplasms, along with endometrioid and clear cell tumors; recent molecular studies suggest this particular tumor is a variant of endometrioid tumor. Discrepancies in nomenclature, definition, and morphology of seromucinous tumors appear to be a source of confusion, for both clinicians and general surgicalpathologists. This review summarizes the clinicopathological features of benign, borderline, and malignant seromucinous tumors, as well as controversies regarding these tumors.

[Borderline Ovarian Tumours: CNGOF Guidelines for Clinical Practice - Imaging]

OBJECTIVE

To determine the place of imaging and the performance of different imaging techniques (transvaginal ultrasound with or without Doppler, scoring, CT, MRI) to differentiate benign tumour, borderline ovarian tumour (BOT) and malignant ovarian tumor. Differentiate the histological subtypes of BOT (serous, sero-mucinous, mucinous) and prediction in imaging of the possibility of conservative treatment.

METHODS

The research was carried out over the last 16 years using the terms "MeSH" based on the query of the Medline® database and supplemented by the review of references contained in the meta-analyzes, systematic reviews and original articles included.

RESULTS

Endo-vaginal and suprapubic ultrasonography is recommended for analysis of an ovarian mass (grade A). In the case of ultrasound by a referent, subjective analysis is the recommended technique (grade A). In case of echography by a non-referent, the use of "Simple Rules" is recommended (grade A) and should be best combined with subjective analysis to rejoin the performance of a sonographer refer (grade A). In cases of undetermined ovarian lesions in endovaginal ultrasound and suprapubic ultrasound, it is recommended to perform a pelvic MRI (grade A). The MRI protocol should include T2, T1, T1 sequences with fat saturation, diffusion, injected dynamics, and after gadolinium injection (grade B). To characterize an MRI-adnexal image, it is recommended to include a risk score for malignancy (ADNEX-MR/O-RADS) (grade C) in the report and to formulate an anatomopathological hypothesis (Grade C). The predictive signs of benignity in front of a cyst with endocystic vegetations are the low number, the small size, the presence of calcifications and the absence of Doppler flow in case of size greater than 10mm in echography (LP 4) and a curve of type 1 MRI (LP4). MRI is recommended for suspicious lesions of BOT in ultrasound (grade B) or indeterminate lesions in ultrasound (grade A). There is no data to support the usefulness of CT or PET-CT for BOT. Morphological criteria in ultrasound and MRI exist to differentiate BOT from invasive tumors regardless of grade (NP 2). Pelvic MRI is recommended to characterize a tumor suggestive of ultrasound BOT (grade C). No recommendations can be made about the use of combined ultrasound, biological, and menopausal status scores for the diagnosis of BOT. The diagnostic performance of imaging to detect peritoneal implants of BOT is not known. The assessment of the invasiveness of peritoneal implants of imaging BOT has not been evaluated. The association of macroscopic signs in MRI makes it possible to differentiate the different subtypes - serous, sero-mucinous and mucinous (intestinal type) - of BOT, despite the overlap of certain presentations (LP3). The analysis of macroscopic MRI signs must be performed to differentiate the different subtypes of TFO (grade C). No recommendation can be made on imaging prediction of the possibility of conservative BOT treatment.

Uncommon borderline ovarian tumours: A clinicopathologic study of seventeen patients

Objective

To evaluate uncommon types of borderline ovarian tumors (BOT) and define the clinical, surgical, and pathologic features.

Material and Methods

Seventeen patients who were treated in our hospital between 1990 and 2017 were identified. Patients’ data were collected from the gynecologic oncology clinic electronic database, patients’ files, and pathology reports. Conservative surgery was defined as preservation of the uterus and at least part of one ovary.

Results

The mean age was 47 (range, 22-70) years. Based on histopathologic tumor type, there was mixed tumor in five (29.4%) patients, endometrioid-type in nine (52.9%), seromusinous-type in two (11.8%), and Brenner-type in one (5.9%). Conservative surgery was performed in 4 patients. Two patients with endometrioid BOT had synchronous endometrial pathology, including one (11%) patient with endometrial cancer, one (11%) with endometrial hyperplasia without atypia, and 3 (33%) patients had endometriosis. The median follow-up was 19 (range, 1-137) months. No recurrence was observed during the follow-up period.

Conclusion

In our small volume case series, it could be said that non-serous/non-mucinous BOT has excellent prognosis. However, endometrial pathology should be checked in endometrioid type.

Endometriosis-associated ovarian neoplasia

This article reviews the most relevant pathological and molecular features of ovarian tumours that are associated with endometriosis. Endometriosis is a common condition, affecting 5-15% of all women, and it has been estimated that 0.5-1% of cases are complicated by neoplasia. The most common malignant tumours in this setting are endometrioid adenocarcinoma and clear cell adenocarcinoma, each accounting for approximately 10% of ovarian carcinomas in Western countries. A minority of cases are associated with Lynch syndrome. These carcinomas are often confined to the ovaries at presentation in which case they have relatively favourable outcomes. However, high-stage tumours, particularly clear cell carcinomas, generally have a poor prognosis and this partly reflects relative resistance to current treatment. Histological diagnosis is straightforward in the majority of cases but some variants, for example endometrioid carcinomas with sex cord-like appearances or oxyphil cells, may create diagnostic difficulty. Similarly, clear cell carcinomas can show a range of architectural and cytological patterns that overlap with other tumours, both primary and metastatic, involving the ovaries. Endometriosis-associated borderline tumours are less common, and they often show mixed patterns of differentiation (seromucinous tumours). Atypical endometriosis may represent an intermediate step in neoplastic progression and some of these lesions demonstrate immunohistological and molecular alterations similar to those observed in endometriosis-related tumours. ARID1A mutations are relatively common in all of these tumours, but each has additional characteristic molecular alterations which are likely to be of increasing clinical relevance as targeted therapies are developed. Less is known of the pathogenesis of rarer endometriosis-associated ovarian tumours including endometrioid stromal sarcoma, mesodermal (Müllerian) adenosarcoma, and carcinosarcoma. This article also briefly reviews the issue of synchronous endometrioid carcinomas of the endometrium and the ovary, including the most recent developments on pathogenesis.

Differentiation of Seromucinous Borderline Tumor from Serous Borderline Tumor on MR Imaging

PURPOSE

Seromucinous borderline tumor (SMBT) is a newly categorized ovarian tumor in the 2014 revised World Health Organization (WHO) classification. SMBT is similar to serous borderline tumor (SBT) on MRI reflecting their pathological findings. This study was conducted to demonstrate the usefulness of MRI findings and quantitative values for differentiating SMBT from SBT.

METHODS

This retrospective study examined 23 lesions (20 patients) from SMBT and 26 lesions (22 patients) from SBT. The following quantitative values were evaluated using receiver-operating characteristics analysis: overall and solid portion sizes, intracystic fluid signal intensity (SI) ratio compared with skeletal muscle on T₁weighted image (T₁WI) and T₂weighted image (T₂WI), contrast enhancement (CE) ratio, and mean and minimum apparent diffusion coefficient values of the solid portion. Two radiologists evaluated the prevalence of MRI finding characteristics of SMBT and SBT. The SI of the intracystic fluid on T₁WI and T₂WI and the association with endometriosis were evaluated visually.

RESULTS

The CE ratio was significantly higher in SBT (P = 0.007). It achieved the highest area under the curve (AUC) (0.739). The fluid SI ratio on T₁WI was higher in SMBT (P = 0.036, AUC = 0.676). Exophytic growth of the solid portion was observed only in SBT (P = 0.011). Intracystic fluid SI of SMBT was higher on T₁WI and lower on T₂WI in visual evaluation (P = 0.008 and 0.007, respectively). Findings suggesting endometriosis were observed more frequently in SMBT patients (P = 0.019).

CONCLUSION

Higher CE ratio of the solid portion and exophytic growth were findings suggesting SBT. Higher intracystic fluid SI on T₁WI and lower SI on T₂WI suggested SMBT. MRI findings suggesting endometriosis favored the diagnosis of SMBT.

Ovarian borderline tumors in the 2014 WHO classification: evolving concepts and diagnostic criteria

Borderline ovarian tumors (BOT) are uncommon but not rare epithelial ovarian neoplasms, intermediate between benign and malignant categories. Since BOT were first identified >40 years ago, they have inspired controversies disproportionate to their incidence. This review discusses diagnostic criteria for the histologic subtypes of BOT, highlighting areas of diagnostic challenges, ongoing controversies, and changes in terminology implemented by the recent 2014 WHO Classification of Tumours of the Female Genital Organs. Emerging knowledge supports the notion that subtypes of borderline ovarian tumors comprise distinct biologic, pathogenetic, and molecular entities, precluding a single unifying concept for BOT. Serous borderline tumors (SBT) share molecular and genetic alterations with low-grade serous carcinomas and can present at higher stages with peritoneal implants and/or lymph node involvement, which validates their borderline malignant potential. All other (non-serous) subtypes of BOT commonly present at stage I confined to the ovary(ies) and are associated with overall survival approaching that of the general population. An important change in the WHO 2014 classification is the new terminology of non-invasive implants associated with SBT, as any invasive foci (previously called “invasive implants”) are now in line with their biological behavior considered peritoneal low-grade serous carcinoma (LGSC). The controversy regarding the terminology of non-serous borderline tumors, called by some pathologists “atypical proliferative tumor” in view of their largely benign behavior, has not been resolved. The concepts of intraepithelial carcinoma and microinvasion may evolve in further studies, as their presence appears to have no prognostic impact and is subject to considerable inter-observer variability.

Pathology of borderline and invasive cancers

Epithelial ovarian tumors are heterogeneous neoplasms primarily classified according to cell type. They are further subdivided into benign, borderline, and malignant (carcinomas), and this subdivision is very important as it correlates with behavior. Borderline ovarian tumors show epithelial proliferation higher than that seen in their benign counterparts and variable nuclear atypia; however, in contrast to carcinomas, there is no destructive stromal invasion, and their prognosis is much better. Ovarian carcinomas are the most common ovarian cancers and the most lethal gynecological malignancies. On the basis of histopathology and molecular genetics, they are divided into five types (high-grade serous (70%), endometrioid (10%), clear cell (10%), mucinous (3%), and low-grade serous carcinomas (<5%)), which are morphologically diverse and account for over 95% of cases. These tumors are essentially distinct diseases, as indicated by differences in epidemiological and genetic risk factors, precursor lesions, patterns of spread, molecular alterations, response to chemotherapy, and prognosis. For a successful specific treatment, reproducible histopathological diagnosis of the tumor cell type is critical.

Diagnostic performance of MR imaging findings and quantitative values in the differentiation of seromucinous borderline tumour from endometriosis-related malignant ovarian tumour

OBJECTIVES

To evaluate the diagnostic performance of quantitative values and MRI findings for differentiating seromucinous borderline tumours (SMBTs) from endometriosis-related malignant ovarian tumours (MT).

METHODS

This retrospective study examined 19 lesions from SMBT and 84 lesions from MT. The following quantitative values were evaluated using receiver-operating characteristic analysis: overall and solid portion sizes, fluid signal intensity (SI), degree of contrast-enhancement, and mean and minimum apparent diffusion coefficient (ADC) values of the solid portion. Two radiologists independently evaluated four MRI findings characteristic of SMBT, fluid SI on the T1-weighted image and SI of the solid portion on diffusion-weighted image. The diagnostic values of these findings and interobserver agreement were assessed.

RESULTS

For diagnosing SMBT, the mean ADC value of the solid portion showed the greatest area under the curve (0.860) (cut-off value: 1.31 × 10^-3 mm²/s, sensitivity: 1.00, specificity: 0.61). The T2-weighted image (T2WI) high SI solid portion was the most useful finding, with high specificity and interobserver agreement (sensitivity, 0.58; specificity, 0.95-0.96, kappa = 0.96), followed by T2WI low SI core (sensitivity, 0.48-0.63; specificity, 0.98, kappa = 0.68).

CONCLUSION

Mean ADC values of the solid portion, T2WI high SI solid portion, and T2WI low SI core were useful for differentiating SMBT from MT.

KEY POINTS

• SMBT is a newly categorised ovarian tumour often associated with endometriosis. • Differentiation of SMBT from endometriosis-related malignant ovarian tumour is clinically important. • Diagnostic performances of quantitative values and MRI findings were evaluated. • Mean ADC value of the solid portion was the most useful value. • "T2WI high SI solid portion" was the most useful MRI finding.

Pelvic recurrence of an ovarian seromucinous borderline tumor detected by vaginal cytology: A case report and review of the literature

Seromucinous borderline tumors are typically confined to the ovaries and rarely relapse after surgery. We report the case of a woman with a seromucinous borderline tumor with peritoneal implant at the Douglas pouch, who was affected by a recurrent tumor at the vaginal stump 2 years and 6 months after the primary surgery. The recurrent lesion was detected by vaginal cytology. Histology of the recurrent lesion showed perineural infiltration, and progression to low-grade adenocarcinoma was suggested. After the second surgery, vaginal cytology showed that the tumor cells remained positive. At postoperative follow-ups of ovarian borderline tumors, an examination of the specific region where recurrence is likely to occur can contribute to the early detection of tumor relapse. Diagn. Cytopathol. 2016;44:912-916. © 2016 Wiley Periodicals, Inc.

[Mucinous ovarian neoplasms. Prognostically mostly excellent, infrequently a wolf in sheep's clothing]

Mucinous ovarian neoplasms represent the second largest group of epithelial ovarian tumors after serous neoplasms, of which benign cystadenomas constitute more than 80 %. Mucinous cystadenomas and carcinomas cannot be distinguished by the clinical features or the mean age of onset of the disease. They typically occur unilaterally, are confined to the adnexae (FIGO stage I) and clinically present with non-specific abdominal symptoms or are diagnosed by chance. The mean age of disease onset is around 50 years old. The prognosis is excellent. Implants, peritoneal metastases and bilateral occurrence of ovarian mucinous neoplasms should lead to the suspicion of metastasis particularly from a gastrointestinal tumor. Neither microinvasion defined as a maximum extent of invasion of 5 mm, nor intraepithelial carcinoma characterized by high grade atypia without invasion, affect the prognosis of mucinous borderline tumors. Mucinous carcinomas typically show confluent glandular, expansile growth that leads to a labyrinth-like pattern. A destructive infiltrative or nodular growth pattern, however, should lead to the consideration of metastasis. Mural nodules that may reveal a spindle cell sarcomatous or anaplastic carcinomatous pattern occur infrequently in mucinous and do not affect the prognosis. Pax8 positivity is indicative of a primary ovarian neoplasm. In this case, however, mucinous tumors associated with teratomas may show the colonic immunoreaction pattern (CK7-/CK20+/CDX2+). The rare mucinous tumors with endocervical differentiation are now designated as seromucinous tumors and consist of two or more distinct cell types, are frequently associated with endometriosis and seem to show a molecular genetic relationship to endometrioid neoplasms.

Recent concepts of ovarian carcinogenesis: type I and type II

Type I ovarian tumors, where precursor lesions in the ovary have clearly been described, include endometrioid, clear cell, mucinous, low grade serous, and transitional cell carcinomas, while type II tumors, where such lesions have not been described clearly and tumors may develop de novo from the tubal and/or ovarian surface epithelium, comprise high grade serous carcinomas, undifferentiated carcinomas, and carcinosarcomas. The carcinogenesis of endometrioid and clear cell carcinoma (CCC) arising from endometriotic cysts is significantly influenced by the free iron concentration, which is associated with cancer development through the induction of persistent oxidative stress. A subset of mucinous carcinomas develop in association with ovarian teratomas; however, the majority of these tumors do not harbor any teratomatous component. Other theories of their origin include mucinous metaplasia of surface epithelial inclusions, endometriosis, and Brenner tumors. Low grade serous carcinomas are thought to evolve in a stepwise fashion from benign serous cystadenoma to a serous borderline tumor (SBT). With regard to high grade serous carcinoma, the serous tubal intraepithelial carcinomas (STICs) of the junction of the fallopian tube epithelium with the mesothelium of the tubal serosa, termed the “tubal peritoneal junction” (TPJ), undergo malignant transformation due to their location, and metastasize to the nearby ovary and surrounding pelvic peritoneum. Other theories of their origin include the ovarian hilum cells.

MRI appearances of mucinous borderline ovarian tumors: pathological correlation

PURPOSE

The purpose of this study is to evaluate the MRI features of mucinous borderline ovarian tumors (MBOT).

MATERIALS AND METHODS

MRI morphology of 30 MBOT proven MBOT by surgery and pathology was retrospectively studied and correlated with the histopathological findings. On MRI, tumors were classified into three morphological categories: (i) unilocular cyst in five (17%) tumors. (ii) multilocular cyst in 23 (76%) tumors. (iii) solid mass in 2 (7%) tumors. MRI features of tumors were identified including the multilocularity (23/30, 77%), honeycomb loculi (15/30, 50%), signal discrepancy (different signal intensity on T1WI and T2WI) (19/30, 63%), thickened wall or septa (>3 mm) (16/30, 53%).

RESULTS

Intestinal type and endocervical type of MBOT, two distinctly histologic subtypes, were found in 20 (67%) and 10 (33%) tumors respectively. There were a higher prevalence of multilocularity (P = 0.026), honeycomb loculi (P = 0.025), and signal discrepancy (P = 0.024) in intestinal type than endocervical type of MBOT.

CONCLUSION

Typical MRI features of MBOT are large multilocular tumors with honeycomb loculi, heterogeneous signal intensity of the loculi, and thickened wall or septa.

Claudin-18 overexpression in intestinal-type mucinous borderline tumour of the ovary

AIMS

Mucinous borderline tumours of the ovary are subclassified as intestinal-type (IMBT) and endocervical-like (EMBT), which differ in their clinicopathological features. In this study, we attempted to elucidate characteristics of the mucinous epithelium in each subtype.

METHODS AND RESULTS

The expression of claudin-18, a marker of gastric differentiation, MUCs, CDX2, CK7, CK20, oestrogen receptor (ER), progesterone receptor (PgR), CA-125 and vimentin in IMBTs (n = 54), EMBTs (n = 25) and serous borderline tumours (SBTs) (n = 22) were compared by immunohistochemistry. Claudin-18 positivity was identified in 98% of the IMBTs, whereas only 4% of the EMBTs were claudin-18-positive. Expression of intestinal markers such as CDX2 and MUC2 was relatively infrequent in IMBTs (48% and 33%, respectively). Müllerian-lineage markers such as ER, PgR and vimentin were expressed rarely in IMBTs, while most EMBTs and SBTs were positive for these markers. Hierarchial clustering revealed a close association between EMBTs and SBTs, while IMBTs were clearly separate.

CONCLUSIONS

Claudin-18 positivity is a specific phenotype that is characteristic of IMBTs. Frequent and diffuse expression of gastric markers, along with less frequent and usually focal expression of intestinal markers, suggests that IMBTs are essentially composed of gastrointestinal-type mucinous epithelium (gastric-type epithelium with a variable degree of intestinal differentiation).

Diagnosis, treatment, and follow-up of borderline ovarian tumors

Borderline ovarian tumors represent a heterogeneous group of noninvasive tumors of uncertain malignant potential with characteristic histology. They occur in younger women, are present at an early stage, and have a favorable prognosis, but symptomatic recurrence and death may be found as long as 20 years after therapy in some patients. The molecular changes in borderline ovarian tumors indicate linkage of this disease to type I ovarian tumors (low-grade ovarian carcinomas). The pathological stage of disease and subclassification of extraovarian disease into invasive and noninvasive implants, together with the presence of postoperative macroscopic residual disease, appear to be the major predictor of recurrence and survival. However, it should be emphasized that the most important negative prognostic factor for recurrence is just the use of conservative surgery, but without any impact on patient survival because most recurrent diseases are of the borderline type-easily curable and with an excellent prognosis. Borderline tumors are difficult masses to correctly preoperatively diagnose using imaging methods because their macroscopic features may overlap with invasive and benign ovarian tumors. Over the past several decades, surgical therapy has shifted from a radical approach to more conservative treatment; however, oncologic safety must always be balanced. Follow-up is essential using routine ultrasound imaging, with special attention paid to the remaining ovary in conservatively treated patients. Current literature on this topic leads to a number of controversies that will be discussed thoroughly in this article, with the aim to provide recommendations for the clinical management of these patients.

"Piling up" clear cells in müllerian-type mucinous and mixed cell-type borderline tumor do not represent concomitant clear cell neoplasms

The nature of "piling up" proliferation of clear cells in müllerian mucinous/mixed borderline tumor has not been well characterized. The purpose of this study was to clarify whether or not such clear cells represent concomitant clear cell neoplasms. First, we carefully reviewed hematoxylin and eosin slides taken from 139 ovarian tumors diagnosed as clear cell carcinoma (112 cases) and müllerian mucinous/mixed borderline tumor (27 cases) to clarify (1) the frequency of piling-up clear cells in müllerian mucinous/mixed borderline tumor and (2) the frequency of the coexistence of typical clear cell carcinoma and müllerian mucinous/mixed borderline tumor. Second, we investigated the immunohistochemical expression of estrogen receptor, hepatocyte nuclear factor-1β, and glypican-3 in proliferating clear cells in both tumors. We identified piling-up clear cells in 56% of müllerian mucinous/mixed borderline tumors. Such clear cells lacked the severe nuclear atypia, complex branching, and dense hyalinized cores of typical clear cell carcinoma. We did not find coexistence of typical clear cell carcinoma and müllerian mucinous/mixed borderline tumor in any tumors. Piling-up clear cells and endocervical-like mucinous cells were positive for estrogen receptor but negative for hepatocyte nuclear factor-1β and glypican-3. Most clear cell carcinomas showed a hepatocyte nuclear factor-1β-positive/estrogen receptor-negative immunophenotype, and about half of them were glypican-3 positive. In conclusion, piling-up clear cells in müllerian mucinous/mixed borderline tumor do not represent concomitant clear cell neoplasms because clear cell carcinoma and müllerian mucinous/mixed borderline tumor hardly ever coexist and because such clear cells in both tumors are immunophenotypically distinct.

Recommendations of the Fertility Task Force of the European Society of Gynecologic Oncology about the conservative management of ovarian malignant tumors

In young patients with borderline ovarian tumor a conservative treatment approach does not seem to have a significant impact on survival, and the outcome regarding fertility is good in general. It can be considered even if noninvasive peritoneal implants are discovered at the time of the initial surgery. In contrast, in patients with epithelial ovarian cancer, conservative surgery should be considered only in adequately staged patients, with a stage IA grade 1 (and probably 2) serous, mucinous or an endometrioid tumor, including a careful follow-up. Such an approach could also probably be discussed in stage IC grade 1 disease.In patients with nonepithelial malignant ovarian tumors, conservative surgery is also feasible, particularly in patients with malignant germ cell tumors because of their high chemosensitivity leading to an excellent prognosis in general.

Tumor-infiltrating neutrophils in pancreatic neoplasia

The interaction between tumor cells and inflammatory cells has an important role in cancer initiation and progression; however, this interaction has not been systematically investigated in pancreatic neoplasia. In this study, the presence of tumor-infiltrating neutrophils within and/or adjacent to neoplastic cells was investigated in pancreatic neoplasms. Areas with >10 tumor-infiltrating neutrophils/100 epithelial cells were arbitrarily classified as positive. Those with 11-15 tumor-infiltrating neutrophils were considered 'borderline' while those with >15 tumor-infiltrating neutrophils were considered 'significant'. Among 363 invasive ductal carcinomas, 15 showed significant tumor-infiltrating neutrophils (8 were micropapillary carcinomas and 7 were undifferentiated carcinomas). Of 19 mucinous cystic neoplasms with a carcinomatous high-grade papillary component, 11 showed significant tumor-infiltrating neutrophils (mean, 25; range, 14-63 tumor-infiltrating neutrophils). Among intraductal papillary mucinous neoplasms, significant tumor-infiltrating neutrophils were identified in 4/16 pancreatobiliary type, but were uncommon in other types (1/11 oncocytic and 1/23 intestinal types had borderline tumor-infiltrating neutrophils, and 0/10 gastric type had tumor-infiltrating neutrophils). Non-carcinomatous (low-grade and non-papillary) components of these neoplasms did not have tumor-infiltrating neutrophils. Tumor-infiltrating neutrophils were not striking in neuroendocrine tumors (40), serous cystadenomas (18), acinar cell carcinomas (9) or solid-pseudopapillary neoplasms (8). In conclusion, significant tumor-infiltrating neutrophils are uncommon in pancreatic ductal adenocarcinoma, and when they occur it is typically in the micropapillary and undifferentiated types with a known poor prognosis. Among pre-invasive neoplasia, tumor-infiltrating neutrophils show a predilection for papillary in-situ carcinomas of mucinous cystic neoplasms, or less commonly, pancreatobiliary-type intraductal papillary mucinous neoplasms (both of which express cell surface-associated mucin 1 (MUC1)). MUC1 expression by these tumors may have biologic implications, considering its recently established relationship with inflammatory cells in carcinogenesis, and the differential expression of mucins in pancreatic neoplasia. Larger studies are needed to investigate the association between tumor-infiltrating neutrophils and pancreatic neoplasms and their role in their clinical behavior.

Morphological subtypes of ovarian carcinoma: a review with emphasis on new developments and pathogenesis

Ovarian carcinomas comprise a heterogeneous group of neoplasms, the four most common subtypes being serous, endometrioid, clear cell and mucinous. In recent years, our understanding of the underlying pathogenesis and initiating molecular events in the different tumour subtypes has greatly increased, and although ovarian carcinoma is often considered clinically as one disease, there is now a much greater realisation that the various subtypes have a different natural behaviour and prognosis. At present, adjuvant therapy is mainly dependent upon tumour stage and grade rather than type; however, this is likely to change in the future with the development of new chemotherapeutic agents and targeted therapies and clinical trials are necessary to evaluate the efficacy of different agents in clear cell, mucinous and low grade serous carcinomas, neoplasms which are considered relatively resistant to traditional chemotherapeutic regimes. In this review, the major subtypes of ovarian carcinoma are discussed. It is now firmly established that there are two distinct types of ovarian serous carcinoma, low grade and high grade, the former being much less common and arising in many cases from a serous borderline tumour. Low grade and high grade serous carcinoma represent two distinct tumour types with a different underlying pathogenesis rather than low grade and high grade variants of the same neoplasm. Both are usually advanced stage (stage III or IV) at diagnosis. B-raf and k-ras mutations are important molecular events in low grade serous carcinomas while high grade serous carcinomas are almost always associated with TP53 mutation. There is now emerging and compelling evidence that many high grade serous carcinomas (by far the most common subtype of ovarian carcinoma) actually arise from the epithelium of the distal fallopian tube. Future studies regarding the initiating molecular events in the development of this aggressive neoplasm should concentrate on this site. Primary ovarian mucinous carcinomas are uncommon, almost always unilateral and stage I, and largely of so-called intestinal or enteric type. Most arise in a stepwise manner from a pre-existing mucinous cystadenoma and mucinous borderline tumour. Endometrioid and clear cell carcinomas typically present as low stage neoplasms and in many, or most, cases arise from endometriosis; the former are usually well differentiated and there is now evidence that the majority of neoplasms reported in the past as high grade endometrioid carcinoma are of serous type. WT1 is useful in this regard since it is a relatively specific marker of a serous phenotype. It is recommended that different subtypes of ovarian carcinoma are graded using different systems rather than employing a universal grading system.

Immunohistochemistry in the distinction between primary and metastatic ovarian mucinous neoplasms: Table 1

The distinction between a primary and metastatic mucinous carcinoma within the ovary may be problematic. In most cases, the distinction can be made by careful pathological examination encompassing both the gross and microscopic findings and taking into account the distribution of the disease. However, immunohistochemistry may be of value in certain scenarios. In this review, I discuss the value of markers in the distinction between primary ovarian mucinous neoplasms and metastatic mucinous carcinomas from the colorectum, appendix, pancreas, biliary tract, stomach and cervix, the most common primary sites which give rise to metastatic mucinous carcinoma within the ovary. There is a significant degree of immunophenotypic overlap between primary ovarian mucinous neoplasms and metastatic mucinous carcinomas from the gastrointestinal tract, especially the upper gastrointestinal type; this is because most primary ovarian mucinous carcinomas and borderline tumours are of so-called intestinal or enteric type and exhibit some degree of positivity with enteric markers. Mullerian type primary ovarian mucinous neoplasms also exist and exhibit distinct immunohistochemical differences to the more common intestinal type.

Endocervical-like (Müllerian) mucinous borderline tumours of the ovary are frequently associated with the KRAS mutation

AIMS

  Clinicopathological aspects of the endocervical-like mucinous borderline tumour of the ovary (EMBT), including higher frequencies of bilaterality, endometriosis and hormone receptor reactivity, and often admixtures of various Müllerian-type epithelia, closely resembles endometrioid tumour more than mucinous borderline tumour of the intestinal type (IMBT). Thus, the aims of this study were to determine whether EMBT is really a subtype of mucinous borderline tumours, as shown in the current classification system, and to determine the best classification for EMBT.

METHODS AND RESULTS

  The clinicopathological and immunohistochemical features of 17 EMBTs were analysed, including oestrogen receptor (ER), progesterone receptor (PR), PTEN, cytokeratins (CK) 7 and 20, and β-catenin. Additionally, mutational analyses of the KRAS (exon 1) and PTEN genes (all nine exons) were performed in all cases, and the results were compared with literature findings for IMBT and endometrioid tumours. Twelve patients (71%) were confirmed histologically to have endometriosis in one or both ovaries. In seven cases, gradual transitions from endometriotic foci to the EMBT were identified. Immunohistochemically, all cases were reactive for ER and PR, with no nuclear expression of β-catenin. CK7 positivity was strong in all patients, whereas there was no reactivity for CK20. PTEN reactivity was diffuse in the nuclei of epithelial and underlying stromal cells. Sixty-nine per cent showed KRAS mutations in exon 1 and codon 12, but no PTEN mutation was identified in any of the nine exons.

CONCLUSION

  Our study suggests that EMBT has features of both mucinous and endometrioid tumours and is an additional tumour type arising in endometriosis. While clinicopathological features of EMBTs are closer to endometrioid tumours, they still have molecular characteristics closer to IMBTs.

Squamous cell carcinoma of the ovary arising from a mucinous cystic tumor of endocervical (müllerian) type

Primary squamous cell carcinoma of the ovary is extremely rare. We studied a 58-year-old woman in whom a keratinizing squamous cell carcinoma of the ovary had arisen from a mucinous cystic tumor of endocervical (müllerian) type. The tumor was interpreted initially as a transitional cell carcinoma of the ovary with marked squamous differentiation, but there was no evidence of either transitional cell carcinoma or malignant Brenner tumor. Furthermore, features of dermoid cyst (mature cystic teratoma), endometriosis, or adenosquamous carcinoma were not seen. The mucinous columnar epithelial component was largely benign and only focally proliferative or borderline. As found typically in endocervical (müllerian) mucinous tumors, numerous polymorphonuclear leukocytes were seen in the stroma and the neoplastic mucinous epithelium.

Prognostic factors of a large retrospective series of mucinous borderline tumors of the ovary (excluding peritoneal pseudomyxoma)

BACKGROUND

To determine the prognosis and prognostic factors in a large series of mucinous borderline tumors of the ovary (MBOT).

MATERIALS AND METHODS

A retrospective review of patients with MBOT treated or referred to our institution. Three inclusion criteria were defined: (1) centralized histological review by our expert pathologist, (2) exclusion of peritoneal pseudomyxoma and any synchronous malignant tumor in the abdominal cavity, and (3) available data on the management and outcomes of patients.

RESULTS

From 1997 to 2004, 97 patients fulfilled inclusion criteria (95 stage I and 2 stage II disease). Of these, 9 patients had endocervical-like subtypes, 8 patients had stromal microinvasion, and 24 had intraepithelial carcinoma. Radical and conservative surgeries were performed, respectively, in 28 and 69 patients. After a median follow-up of 48 months, 13 patients had developed 14 recurrences: 7 were borderline and 7 were invasive lesions. The probability of recurrence in the form of carcinoma 5 and 10 years after the diagnosis was, respectively, 9 and 13%. The only prognostic factor for recurrence attaining statistical significance was the use of a cystectomy (compared with other surgeries relative risk [RR] = 5.6; P = 0.003; compared with salpingo-oophorectomy RR = 5.5; P = 0.012).

CONCLUSIONS

In the present series of 97 MBOT, mainly early-stage disease and excluding peritoneal pseudomyxoma, the cumulative risk of recurrence in the form of invasive carcinoma at 10 years was 13%. MBOT do not appear to be such a "safe" disease. The only prognostic factor for recurrence was the use of a cystectomy, suggesting that a salpingo-oophorectomy should be preferred in cases of conservative treatment.

Intestinal type and endocervical-like ovarian mucinous neoplasms are immunophenotypically distinct entities

Ovarian mucinous neoplasm (OMN) is traditionally classified as either intestinal type or endocervical-like subtypes. The 2 subtypes represent different clinicopathologic characteristics. The immunophenotype of the 2 subtypes has not been adequately investigated. In this study, we investigated 14 intestinal type OMNs (borderline and adenocarcinoma) and 12 endocervical-like OMNs (borderline and adenocarcinoma) for their expression of PDX-1, CDX-2, CA-125, CK7, CK20, WT-1, D2-40, and TTF-1. We also included 15 colorectal adenocarcinomas metastatic in the ovary, as they may occasionally mimic OMN. The intestinal type OMNs were positive for PDX-1 (100%), CK7 (100%), CK20 (100%), CDX-2 (29%), whereas were negative for CA-125. The endocervical-like OMNs were positive for CA-125 (100%) and CK7 (100%), whereas were negative for CK20, PDX-1, and CDX-2. Metastatic colorectal adenocarcinomas were positive for CK20 (100%), CDX-2 (100%), and PDX-1 (33%), whereas were negative for CA-125 and CK7. All of the intestinal type and endocervical-like OMNs as well as metastatic colorectal adenocarcinomas were negative for WT-1, D2-40, and TTF-1. Our results demonstrated that the intestinal type and endocervical-like OMNs are immunophenotypically distinct entities. The 2 subtypes can be separated from metastatic colorectal adenocarcinoma by the different immunohistochemical profile of PDX-1, CA-125, CK7, CK20, and CDX-2. In the work-up of mucinous adenocarcinoma in the ovary or abdominal cavity, caution should be exercised in interpreting the possible primary site on the basis of the immunohistochemical profiles.

Ovarian adenosarcoma with extensive deciduoid morphology arising in endometriosis: a case report

A case of müllerian adenosarcoma arising in ovarian endometriosis is reported in which the whole of the mesenchymal component exhibited striking deciduoid morphology, a phenomenon that has not been previously described. The patient was not taking hormonal preparations. We discuss the differential diagnosis and the possible pathogenesis of the deciduoid stromal alteration.

Is Stromal Microinvasion in Primary Mucinous Ovarian Tumors With “Mucin Granuloma” True Invasion?

Stromal microinvasion has been recently described in ovarian mucinous borderline tumors (MBTs), leading to proposals for new classifications, including a category of MBTs with stromal microinvasion. This study was conducted to test the validity of this belief. To determine whether stromal microinvasion can be distinguishable from extruded neoplastic epithelium from an adjacent ruptured gland, particularly if accompanied by a mucin granuloma (MG) on hematoxylin and eosin (H&E)-stained sections, we compared the histopathologic features of 138 primary ovarian mucinous tumors, consisting of 81 MBTs, 37 MBTs with stromal microinvasion, 11 intraglandular carcinomas, 2 with microinvasive foci, and 7 mucinous adenocarcinomas with extensive stromal invasion. Immunohistochemical analysis for cytokeratin was performed in 72 cases. Of 77 cases containing MGs, 52% contained "microinvasive foci," consisting of individually scattered epithelial or irregular glandular components in the intervening stroma, as determined by H&E staining. Of the 37 negative cases on H&E, cytokeratin reactivity was detected in 15 additional cases with epithelial/glandular components. Therefore, "stromal microinvasion" can be missed on H&E. All patients with MBT with or without microinvasive foci and localized intraglandular carcinoma with or without microinvasive foci had stage I tumors; none died of tumor-related causes during the follow-up period. Tumor-related deaths were identified only in 5 patients with extensive stromal invasion. This study suggests that some cases of stromal microinvasion in stage I MBTs not accompanied by high grade nuclear atypia represent mucocele-like stromal reaction to ruptured mucinous glands rather than true stromal invasion because isolated tumor cells were exclusively confined to the boundary of MGs and devoid of obvious cellular atypia, and no patient with stromal microinvasion died of tumor-related causes.