Immunohistochemistry in the diagnosis of thymic epithelial neoplasms. Appl Immunohistochem Mol Morphol. 2014;22:479-487. [PMID: 24897066 DOI: 10.1097/pai.0b013e3182a53856]

Rising Threat: Long-Term Trends in the Incidence and Mortality of Thymic Epithelial Tumor

INTRODUCTION

An upward trend in the incidence of thymic epithelial tumors (TETs) has been reported over the past few decades, but because of its rarity, little is currently known about its epidemiological trends. This study examined temporal trends in the incidence and mortality of TETs in the US and explored these trends in population subgroups while investigating important factors that influence their prognosis.

METHODS

A retrospective, population-based study was conducted using nationally representative data from the Surveillance, Epidemiology, and End Results program, and 4979 patients diagnosed with TETs from 2000 to 2020 were evaluated. Associated population data were used to determine age-adjusted incidence and mortality, and 5-year TET-specific mortality (SM). Trends were assessed for the entire cohort, as well as for particular subgroups, including thymoma and thymic carcinoma.

RESULTS

From 2000 to 2020, the overall incidence and mortality of TETs were 2.769 and 1.203 per million person-years, respectively. Both the age-adjusted incidence and mortality of TETs increased over the study period, with increases occurring across almost all ethnic groups, histological subtypes, and stages. Multivariate analysis revealed that age, World Health Organization histological type (B1, B2, and B3 thymoma and thymic carcinoma), Masaoka-Koga stage (IIB and III/IV), maximum tumor diameter (5-10 and > 10 cm), surgery, and chemotherapy were independently associated with TET-SM.

CONCLUSIONS

The incidence and mortality of TETs have steadily increased over time, and these trends might be related to the widespread use of computed tomography for lung cancer screening and the increasing number of TETs found incidentally. The study also identified several important factors independently associated with TET-SM, suggesting that early diagnosis and surgical intervention are critical to achieving good prognoses.

Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

CONTEXT.—

Immunohistochemistry has become a valuable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

OBJECTIVE.—

To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry.

DATA SOURCES.—

Literature review and the author's research data and personal practice experience.

CONCLUSIONS.—

This review article highlights that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoid potential diagnostic errors.

A Painless Right Anterior Neck Mass

A 58-year-old woman presents with a several-week history of a painless right-sided swelling on her anterior neck. What is your diagnosis?

Type A thymoma in a pet rabbit

A 4-y-old, spayed female, mixed-breed domesticated rabbit (Oryctolagus cuniculus domesticus) was presented because of progressive bilateral exophthalmos, with a large mediastinal mass in the cranial thorax. Palliative radiation therapy was elected, and 4 fractions of 5 Gy were delivered twice weekly under general anesthesia using 3-dimensional conformal radiation therapy for a total dose of 20 Gy, guided by an on-board cone beam CT scan. Quality-of-life and respiratory rate improved before sudden death that followed an episode of dyspnea. The overall survival time following initial diagnosis was 93 d, with 68 d after the first dose of radiation. An autopsy was performed, and the mass was diagnosed as a type A thymoma. The diagnosis was confirmed with positive immunohistochemical labeling of the neoplastic cells for cytokeratin 5/6 and cytokeratin 7.

Thymoma: Challenges and Pitfalls in Biopsy Interpretation

The interpretation of biopsy specimens in the diagnosis of thymoma is a subject that is generally not addressed in the literature. Even though the diagnosis of thymoma may seem to be an easy step in the assessment of these tumors, in reality, it is the biopsy specimen interpretation that will be use to determine course of action in any particular patient. It may determine whether a patient is a surgical candidate or on the contrary whether a patient may be benefited the most by medical therapy. In addition, there may be conditions in which all that is required is surgical resection without any further treatment, and that the evaluation of those conditions does not necessarily required the careful pathologic staging that thymomas need. In addition, it is important to highlight that in small biopsies, there are limitations not only in terms of the cellularity and other features that may not be present in such biopsy but also the limitation in term of immunohistochemical interpretation. Herein we have attempted to highlight numerous tumoral conditions that are frequently encountered in the daily practice of mediastinal pathology, some of them pose significant problems in separating them from thymomas. Needles to say, the entire spectrum of mediastinal pathology that may at any given time mimic thymoma is well beyond the scope of this review. Furthermore, we also herein emphasize the need for proper clinical and radiologic information and correlation in order to lead to a better interpretation of the biopsy specimen. The emphasis in this review is on thymoma and their possible pitfall and shortcomings while evaluating small biopsy specimens.

Poorly-differentiated and undifferentiated sarcomas of the mediastinum: a bag of tricks

Mediastinum is a Pandora's Box containing many different structures that can give origin to several cancer types. Our aims are to provide a general framework to make a diagnosis of an undifferentiated pleomorphic sarcoma and to highlight relevant immunohistochemical and molecular techniques that can help in the differential diagnosis. We, therefore, provide a simple three-step algorithmic approach to diagnose pleomorphic sarcoma, emphasizing the role of clinicopathological correlations and advocating for a "relative frequency" method, especially when the material for the diagnosis is scarce, as in small biopsies. In the first place, if clinical and/or radiological features make a non-sarcoma diagnosis more likely, it should be ruled in. Next, even if no specific non-sarcomatous diagnoses are suspected, they should always be ruled out. Lastly, since many sarcomas can have a pleomorphic appearance, specific entities should also be ruled out because their identification might affect prognosis and treatment. We then cover selected immunohistochemical and molecular ancillary tests that can come at hand in the diagnosis, highlighting the pros and cons; in particular the use and the limitations of H3K27me3 immunohistochemistry, the meaning of MDM2 amplification in the mediastinum and the implication of muscle differentiation-either smooth or skeletal-in sarcomas. The main take home messages are to always rule-out more frequent lesion first and always include clinical and radiological information in the diagnostic process.

Trends in the incidence of thymoma, thymic carcinoma, and thymic neuroendocrine tumor in the United States

This study aimed to identify the trends in the incidence of thymic cancer, i.e., thymoma, thymic carcinoma, and thymic neuroendocrine tumor, in the United States. Data from the United States Cancer Statistics (USCS) database (2001-2015) and those from the Surveillance, Epidemiology, and End Results (SEER) database (SEER 9 [1973-2015], SEER 13 [1992-2015], and SEER 18 [2000-2015]) were used in this study. All incidences were per 100,000 population at risk. The trends in incidence were described as annual percent change (APC) using the Joinpoint regression program. Data from the USCS (2001-2015) database showed an increase in thymic cancer diagnosis with an APC of 4.89% from 2001 to 2006, which is mainly attributed to the significant increase in the incidence of thymoma and thymic carcinoma particularly in women. The incidence of thymic cancer did not increase from 2006 to 2015, which may be attributed to the increase in the diagnosis of thymic carcinoma from 2004 to 2015, with a concomitant decrease in thymoma from 2008 to 2015. Before declining, the age-specific incidence of thymic cancer peaked at ages 70-74 years, with a peak incidence at 1.06 per 100,000 population, and decreased in older age groups. The incidence of thymic cancer was higher in men than in women. Asian/Pacific Islanders had the highest incidence of thymoma, followed by black and then white people. The incidence of thymic carcinoma increased from 2004 to 2015, with a concomitant decrease in thymoma from 2008 to 2015. Asian/Pacific Islanders had the highest incidence of thymoma than other races.

Micronodular thymic tumor with lymphoid stroma: A case report and review of the literature

BACKGROUND

Micronodular thymic tumors with lymphoid stroma include micronodular thymoma with lymphoid stroma (MNT) and micronodular thymic carcinoma with lymphoid hyperplasia (MNC), whose micromorphological features are lymphoid stromal hyperplasia and nodular arrangement of tumor epithelial cells. This type of tumor is rare; therefore, the corresponding clinical guidelines, histopathological diagnostic criteria, prognostic factors, and therapeutic regimens have not been established.

CASE SUMMARY

This study covers a novel presentation of MNC in a patient and summarizes the clinicopathological characteristics of this type of tumor by using pooled-analysis methods. Morphologically, this tumor type is a series of benign to malignant pedigrees. We establish the following criteria for the classification of micronodular thymic tumors with lymphoid stroma: (1) Tumor cells with moderate-to-severe dysplasia; (2) Tumor cell mitotic figures > 2/10 high-power fields; (3) Appearance of neoplastic necrosis; (4) No terminal deoxynucleotidyl transferase-positive immature T lymphocytes within the tumor; (5) Tumor cells with a Ki-67 index ≥ 10%; and (6) Tumor cells express CD5. Cases that fall into the borders of two categories in terms of morphology are attributed to atypical MNT. It is proposed that the diagnosis of MNT should be established on the diagnostic criteria mentioned above.

CONCLUSION

Our diagnostic algorithm can effectively distinguish malignant tumors from benign tumors and provides a potent basis for predicting a prognosis, which offers a practical reference for oncologists and pathologists.

Utility of monoclonal PAX8 antibody for distinguishing intrathyroid thymic carcinoma from follicular cell-derived thyroid carcinoma

Follicular cell-derived thyroid carcinomas, including thyroid squamous cell carcinomas (SCCs) and anaplastic carcinomas, are immunoreactive for paired-box gene 8 (PAX8), while non-follicular cell-derived thyroid carcinomas stain negative for the PAX8 antibody. Intrathyroid thymic carcinoma (ITTC) arising from the intrathyroidal ectopic thymus exhibits moderate-to-strong nuclear reactivity for polyclonal PAX8. This is difficult to understand given that PAX8 is not associated with embryonic thymic development. We aimed to determine the diagnostic significance of monoclonal PAX8 antibody in distinguishing ITTCs from follicular cell-derived thyroid carcinomas. Ten ITTCs, 14 poorly differentiated thyroid carcinomas (PDTCs), 14 thyroid SCCs, 7 thymic tissue specimens, 7 thymomas, and 1 thymic carcinoma were analyzed using antibodies against polyclonal and monoclonal PAX8, thyroid transcription factor-1, p63, and CD5. Four ITTCs (40.0%) stained positive for polyclonal PAX8; none stained positive for monoclonal PAX8. All PDTCs and 92.9% of SCCs were immunoreactive for both polyclonal and monoclonal PAX8. All PDTCs, 46.2% of SCCs, and none of the ITTCs were immunoreactive for thyroid transcription factor-1. Eight ITTCs (80.0%), but none of the PDTCs and SCCs, were immunoreactive for CD5. We are the first to show that ITTCs stain negative for monoclonal PAX8. Monoclonal PAX8 is a more reliable marker than polyclonal PAX8 for determining follicular cell origin. We conclude that monoclonal PAX8 is a useful marker for distinguishing ITTCs from PDTCs and SCCs. Monoclonal PAX8 negativity is additional evidence in support of ITTCs not being follicular cell-derived thyroid carcinomas, but having a thymic origin.

Primary clear cell carcinoma of the thymus and literature comparison of features

Clear cell carcinoma arising from the thymus is considered exceedingly rare. It shows aggressive clinical behavior and demonstrates frequent local recurrences as well as widespread metastasis. The detailed clinical data of one patient with thymic clear cell carcinoma were compiled, and a review of relevant reported studies was performed. We summarized the clinical characteristics, pathological diagnosis of the patient and other reported cases. The analysis showed that older male patients were more likely to suffer, and the manifestations included chest pain and dyspnea. Some patients are asymptomatic, with the tumor being discovered during physical examination. Histologically, thymic clear cell carcinoma is composed of lobulated structures arranged in hyperchromatic fibrous stroma; the tumor cells are uniform with obvious nucleoli and clear cytoplasm. To establish the correct diagnosis, consideration and exclusion of metastasis and other original tumors in the differential diagnosis by immunohistochemistry, clinical and radiologic correlation is important.

Prognostic value of immunohistochemical markers in malignant thymic epithelial tumors

BACKGROUND

Thymic epithelial tumors (TET) are rare neoplasms with inconsistent treatment strategies. When researching for molecular pathways to find new therapies, the correlation between specific molecular markers and outcome has only rarely been investigated. The aim of this study was to investigate the correlation between survival, metastatic potential and invasiveness of aggressive subtypes of TET and immunohistochemical markers.

METHODS

Overall survival (OS), disease-free survival (DFS), progression-free survival (PFS) and metastasis-free survival (MFS) of patients with WHO type B2/B3 mixed type thymoma (MT), thymoma type B3 (B3) and thymic carcinoma (TC), undergoing surgery [1998-2013] were determined. Tumor specimens were stained using a tissue microarray (TMA) (CD117, CD5, p63, p40, p21, p27, p53, Bcl-2, Ki67, podoplanin, synaptophysin, PTEN and Pax8). Invasive behavior of primary tumors and the presence of extrathoracic metastases were assessed.

RESULTS

We found in 23 patients included into this study (four MT, ten B3, nine TC) that (I) p21 expression in the cytoplasm significantly correlated with a decrease of OS (P=0.016), PFS (P=0.034) and MFS (P=0.005); (II) MFS was significantly shorter when the combination of p21-low p27-low p53-high was present (P=0.029); and (III) nuclear p27 (P=0.042), Ki-67 (P=0.024) and podoplanin (P=0.05) expression correlated with the presence of extrathoracic metastases.

CONCLUSIONS

The main finding of this study is that cytoplasmic p21 expression negatively influences the outcome of malignant TETs and correlates with metastatic activity. Additionally, selected immunohistochemical markers correlate with the distant metastatic potential of TETs. These results may contribute to the stratification of diagnosis and improvement of treatment strategies for thymic malignancies.