Mucins in prostatic carcinoma

Mucin-producing tumors and tumor-like lesions involving the prostate: a comprehensive review

Mucin-producing tumors of the prostate include both primary and secondary tumors with mucinous differentiation or features involving the prostate gland. These tumors are relatively rare and have variable prognostic and therapeutic implications. Primary mucinous (colloid) adenocarcinoma of the prostate is defined as prostatic adenocarcinoma with mucinous differentiation involving 25% or more of the entire tumor. Another primary tumor of the prostate that may have mucinous features is primary mucin-producing urothelial-type adenocarcinoma of the prostate (mucinous prostatic urethral adenocarcinoma). Primary mucin-producing urothelial-type adenocarcinoma of the prostate is a distinct entity that typically arises from the prostatic urethra possibly from urethritis glandularis or glandular metaplasia with malignant transformation, and it is analogous to adenocarcinoma with mucinous differentiation arising from the urinary bladder. Signet ring cell tumors of the prostate, though rare, may also have mucinous features. Secondary tumors with mucinous differentiation that may involve the prostate include adenocarcinomas of the urinary bladder and colorectum. Pathologists should also be aware of mucin-producing tumor-like lesions involving the prostate, including mucinous metaplasia, and benign Cowper glands that may mimic malignancy. Herein we present an updated and comprehensive review of the clinicopathologic, immunohistochemical, molecular, and prognostic features of mucinous tumors and tumor-like lesions involving the prostate gland, with emphasis on mucinous prostatic adenocarcinoma and its mimickers, including potential diagnostic pitfalls.

Mucinous adenocarcinoma of the prostate does not confer poor prognosis

OBJECTIVES

To report a series of patients with mucinous (colloid) adenocarcinoma (MC) at prostatectomy who were treated at a single institution from 1987 to 2005. MC is a rare form of prostate cancer reported in some cases to have a more aggressive clinical course than conventional adenocarcinoma (AC).

METHODS

Radical prostatectomy specimens with mucinous features were identified from a database of 3613 consecutive patients. Each case was reviewed again by a single pathologist who confirmed the diagnosis of MC in 14 patients. MC was defined by the presence of pools of extracellular mucin in more than 25% of the tumor. Eighteen additional cases were identified in which the mucinous component occupied only a small portion of the tumor and were referred to as AC with focal mucin (AFM). The biochemical and overall survival of 26 patients with MC or AFM who had completed > or = 6 months of follow-up was analyzed using Kaplan-Meier estimates.

RESULTS

No patients with MC or AFM died of disease, and 11 (91.7%) of 12 patients with MC and 9 (64.3%) of 14 patients with AFM were clinically and biochemically free of disease. No significant difference was found in biochemical recurrence or overall survival between those with MC or AFM and a matched group of patients with AC.

CONCLUSIONS

We report what we believe to be the largest published series of cases of MC (n = 14) with a median overall follow-up of 6.4 years. MC appears to behave clinically in a similar fashion to AC, with no statistically significant difference in biochemical failure or survival.

Mucinous differentiation features associated with hormonal escape in a human prostate cancer xenograft

Many theories mention hypersensitive, promiscuous, outlaw or bypass signalling pathways to explain the acquisition of hormone independence in prostate cancer. Hormonal escape of prostate tumours is marked by many biological changes, including mucinous and neuroendocrine differentiation. Since expression of several mucins has been linked to carcinoma tumour progression, we have characterised the expression of mucins at both RNA and protein levels in an in vivo model of prostate cancer in hormonal escape. Using PAC120, a xenograft of a human hormone-dependent prostate tumour, and its hormone-independent variants, we analysed the expression of mucins (MUC1, MUC2, MUC4, MUC5AC, MUC5B, MUC6) by immunohistochemistry or reverse transcriptase (RT)-PCR. While the parental PAC120 tumour was a compact poorly-differentiated tumour of Gleason score 9 (5+4), hormone-independent variants displayed mucinous, neuroendocrine-like or mixed histological changes; these changes were stable through serial transplantations or after testosterone supply. MUC1 mRNA was expressed in both PAC120 and the hormone-independent variants, although at variable levels. All tumours displayed a high and constant expression of MUC2 and no expression of MUC4 mRNA. While MUC1 was expressed in all xenografts whatever their hormone dependence status, MUC2, MUC5B and MUC6 were preferentially expressed in hormone-independent variants. The loss of hormone dependence in this prostate cancer xenograft model is therefore marked by irreversible histological alterations, mucinous or neuro-endocrine, associated with an expression of secretory MUC2, MUC5B and MUC6, independent of the histological differentiation subtype. These data point to mucinous differentiation as an important step in the acquisition of hormone independence in this cancer, and suggest that secretory mucins might participate in an unknown pathway of hormonal escape in prostate cancer.

Contemporary pathology of prostate cancer

In less than 20 years since the introduction of serum PSA and the spring-loaded 18-gauge prostatic biopsy needle, pathologists have adjusted to the limited tissue requirements of narrow needle specimens to apply criteria for diagnosis and grading of prostate cancer, borrowing from lessons learned from radical prostatectomies. Substantial gains have been made during this period in the understanding of precancerous lesions, mimics of malignancy, the criteria for minimal cancer, variants of cancer, and treatment-induced changes. The light microscopic findings remain the criterion standard for diagnosis against which all new techniques should be measured. Numerous findings have proven to be of value, including simple quantitation of histopathologic features, cancer volume, perineural invasion, and others.

Specific staining of tissue components with metal-hematoxylin complexes

The older metal-hematoxylin stains stain a broad spectrum of tissue components. Several recently introduced metal-hematoxylin stains are highly selective. This selectivity is usually bought at the price of severe limitations on the choice of fixative. A very dilute (2 x 10(-4)M) aluminum hematoxylin is selective for nucleic acids in tissues fixed in organic solvents alone. Vanadate hematoxylin is selective for basic proteins in tissues fixed in formaldehyde or mercuric salts. Bismuth hematoxylin is selective for arginine residues and thus for histones and myelin basic protein in tissues fixed in strong acids (Bouin's fluid or SUSA fluid). Zirconyl hematoxylin is selective for acidic mucins. Zirconyl hematoxylin does not restrict the choice of fixative.

Zirconyl hematoxylin: a new stain for acidic mucins

Most stains for acidic mucins are time-consuming to prepare and have poor stability. Zirconyl hematoxylin is easily prepared and works for a year or more. It is made by adding 5 ml freshly-made 0.1% aqueous sodium iodate, 400 mg zirconyl chloride octahydrate, and 40 ml 25% aqueous glycerol, in that order, to 100 mg of hematoxylin in 5 ml of absolute ethanol and stirring for 5 min. Stain 10 min and do not "blue" the stain. Chlorazole black or kernechtrot and fast green are good counterstains. Zirconyl hematoxylin stains acidic mucins violet or red violet, regardless of how they are fixed. It stains the same mucins as alcian blue in mouse and sheep salivary glands. It shows goblet cells in mouse rectum as well as alcian blue. It stains the same stomach regions in a lizard as alcian blue. Like alcian blue and colloidal iron, zirconyl hematoxylin stains the mucin of cancerous prostate, but not normal prostate.

Diagnosis of Cowper's glands on prostate needle biopsy

The presence of normal anatomic structures may be a source of confusion to the pathologist examining prostatic needle biopsies. The morphologic features of Cowper's (bulbourethral) glands incidentally biopsied during transrectal sampling of the prostate have not been described. We reviewed seven cases of Cowper's glands found in prostatic core biopsy specimens. Sections containing Cowper's glands were stained with hematoxylin-eosin, mucicarmine, periodic acid-Schiff's-digest (PAS-D), and antibodies directed at high-molecular-weight cytokeratin (HMWCK), prostate-specific acid phosphatase (PSAP), prostate-specific antigen (PSA), Ulex europaeus agglutinin, and muscle-specific actin. Histologically, Cowper's glands resemble mucinous minor salivary glands entrapped within fascicles of muscle. Lobules of acini composed of cells distended with mucin (mucicarmine and PAS-D positive) were admixed with ducts and ductules composed of hybrid cells with both mucinous and ductular epithelial features. The HMWCK was strongly reactive with the ductular epithelium and demonstrated an attenuated cell lining at the periphery of lobules. The mucinous cytoplasm reacted with U. europaeus, whereas the ductal elements failed to stain. PSAP stains were negative, with PSA positive in most cases. Muscle-specific actin was positive in three cases. Cowper's glands occasionally may be sampled by transrectal needle biopsy. Recognition of this anatomic structure will allow discrimination from low-grade prostatic adenocarcinoma, foamy gland carcinoma, mucinous metaplasia of prostate glands, and atypical glands of undetermined significance.

Neutral and acid mucins and eosinophil and argyrophil crystalloids in carcinoma and atypical adenomatous hyperplasia of the prostate

Neutral and acid mucins and eosinophil and argyrophil crystalloids were studied in the glandular intraluminal contents of 130 prostatic carcinomas (PCa) and 22 atypical adenomatous hyperplasias (AAH). Specimens were studied in the usual extension for diagnostic purposes and considered positive when minimal amounts of mucin or any crystalloid were present. Some amount of altered secretion was seen in 110 PCa (84.6%) and in 17 AAH (77.3%); the similarity of the figures speaks for the close relationship of these lesions. The relative incidences in PCa/AAH were 61.5%/77.3% for neutral mucin, 80%/54.5% for acid mucin (p < 0.01), 25.4%/50% for eosinophil crystalloids (p < 0.02), 44.6%/9.1% for argyrophil crystalloids (p < 0.01) and 57%/36% for a compound secretion. The incidence of eosinophil crystalloids was greater in AAH and inversely proportional to the Gleason grade in PCa. The incidence of acid mucins and argyrophil crystalloids was higher in PCa and directly proportional to the tumour grade in all but the poorly differentiated ones. It is therefore suggested that AAH positive for acid mucins or argyrophil crystalloids be classified in the high grade AAH group.

Mucin expression in atypical adenomatous hyperplasia of the prostate

Prostatic atypical adenomatous hyperplasia (AAH) is a small glandular proliferation that has histological similarities with well-differentiated adenocarcinoma. To determine the histochemical profile of AAH, we assessed the production of total neutral mucin, total acidic mucin, and sulfated acidic mucin in 24 cases of AAH, five cases of Gleason primary pattern 1 and 2 adenocarcinoma, and 29 cases of adjacent benign and hyperplastic prostatic tissue. All specimens were formalin-fixed transurethral resections, and the diagnosis in each was confirmed by evaluation of the keratin 34B-E12 immunoreactive basal cell layer (intact in benign and hyperplastic epithelium, fragmented in AAH, and absent in cancer). The extent of mucin staining was measured semiquantitatively in 10% increments according to the number of stained glands. Neutral mucin was found in all but two cases, and there was no apparent difference in the amount of staining in benign glands, AAH, and cancer (mean number of stained glands, 43%). Total acidic mucin was more common in AAH (63% of cases; mean, 11% of glands) and adenocarcinoma (60% of cases; mean, 30% of glands) than in benign glands (0% of cases). Similarly, nonsulfated acidic mucin was more common in AAH (63% of cases; mean, 12% glands) and adenocarcinoma (60% of cases; mean, 8% of glands) than in benign glands (0% of cases); the pattern and intensity of staining for nonsulfated acidic mucin appeared to be similar to that for total acidic mucin in AAH and cancer. These findings indicate that there is a close relationship in mucin expression between AAH and well-differentiated adenocarcinoma. Identification of acidic mucin should be used cautiously as an adjunct in the diagnosis of adenocarcinoma but is useful in separating some cases of AAH and adenocarcinoma from benign prostatic epithelium.

Acid mucin and high molecular weight cytokeratin in prostatic lesions: evaluation of a combined histochemical and immunohistochemical stain

OBJECTIVE

To evaluate the presence of acid mucins and high molecular weight cytokeratin (KER) in prostatic lesions using a combined histochemical and immunohistochemical stain consisting of Alcian blue at pH 2.5(AB) with a strept-avidin-biotin complex (SAB) staining for KER (SAB-KER).

MATERIALS AND METHODS

Sections were obtained from archival paraffin blocks which included 20 cases of prostatic carcinoma, 30 cases of benign hyperplasia, and five cases of basal cell hyperplasia. Sections were stained for mucosubstances using the AB stain, for KER using SAB-KER and by both AB and SAB-KER, the combined stain (CS).

RESULTS

With the CS stain KER, which is present in the prostatic basal cells, was not detected in malignant glands and in 60% of these cases intraluminal blue-stained acidic mucin was seen. On the other hand, all benign hyperplastic prostatic glands were devoid of intraluminal acidic mucin and showed staining for KER of their basal cells. Areas of basal cell hyperplasia were strongly positive for KER and intraluminal acidic mucin was seen in one case. Each of the stains separately gave similar results to the CS method but the contrast between the areas of carcinoma and hyperplasia was accentuated by the CS, and small foci of carcinoma were easily detected.

CONCLUSION

The combined AB+SAB-KER stain is quicker to perform and allows the simultaneous appraisal of acid mucin and KER.

Diagnostic criteria of limited adenocarcinoma of the prostate on needle biopsy

Over a period of 25 weeks 434 needle biopsy specimens of the prostate were sent to the author for consultation because of diagnostic concerns. The final diagnoses were cancer (69%), benign (13%), atypical but not diagnostic (10%), high grade prostatic intraepithelial neoplasia (PIN) (5%), and miscellaneous (3%). The most common benign entities mimicking cancer were atrophy (29 specimens) and adenosis (19 specimens). The 300 cancer specimens were analyzed further. Architecturally, the presence of small glands between larger benign glands was the most common pattern seen in 80% of carcinomas; haphazard growth patterns, single cells, and cribriform glands were seen less frequently. The following diagnostic features were helpful: nuclear enlargement (77% of specimens); prominent nucleoli (76%); pink acellular intraluminal secretions (53%); amphophilic cytoplasm (39%); blue-tinged mucinous secretions (34%); crystalloids (25%); PIN (13%); mitotic figures (11%); and perineural invasion (3%). The mean and median numbers of malignant glands in this series were 31 and 20, respectively (range, two to 300). Tumors with a Gleason score lower than 6 caused greater diagnostic problems for referring physicians because these tumors had a greater number of malignant glands, yet were still sent in for consultation (P = .0018). Gleason score was positively correlated with prominent nucleoli and amphophilic cytoplasm and inversely correlated with the presence of crystalloids. Prominent nucleoli, which often are quoted as being essential for the diagnosis of prostate cancer, were not seen in 24% of the specimens and seen only rarely in another 25%. The diagnosis of prostate cancer is based on a constellation of features. Even in this series with a limited number of malignant glands, 85% of specimens contained three or more of the above-listed diagnostic features in addition to architectural atypia.

Mucinous adenocarcinoma of the prostate and hormone sensitivity

We report a case of mucinous adenocarcinoma of the prostate treated successfully with androgen ablation followed by laparoscopic lymphadenectomy and total perineal prostatectomy. This case demonstrates that mucinous adenocarcinoma of the prostate may be hormonally sensitive.

Sulfur-rich prostatic intraluminal crystalloids: a surgical pathologic and electron probe x-ray microanalytic study

Prostatic intraluminal crystalloids are irregular eosinophilic, non-birefringent structures increasingly recognized as potential indicators of prostatic malignancy. In a study of 250 randomly selected surgical pathology cases of prostatic tissues none of 50 cases of benign glandular hyperplasia (0%), one of 50 cases of atypical adenomatous hyperplasia, 18 of 50 cases of well-differentiated adenocarcinoma (36%), seven of 50 cases of moderately differentiated adenocarcinoma (14%), and none of 50 cases of poorly differentiated adenocarcinoma (0%) revealed intraluminal crystalloids. A histochemical and immunohistochemical staining panel indicated that the crystalloids were nonproteinaceous. Crystalloids were stained intensely with phosphotungstic acid hematoxylin and did not stain for prostatic-specific antigen or hemoglobin. Crystalloids were clearly differentiated from prostatic corpora amylacea on light microscopy, histochemistry, scanning, and transmission electron microscopy. Electron probe x-ray microanalysis of 10 cases of crystalloids revealed uniform high sulfur peaks and small sodium peaks. We conclude that intraluminal crystalloids are associated more frequently with low-grade prostatic adenocarcinoma, may occur in benign tissue bordering adenocarcinoma, are predominantly composed of inorganic sulfur, and their presence in benign and atypical prostate biopsies may be of pathologic significance and should warrant further clinical investigation and possibly repeat biopsy.

Mucins in prostatic intra-epithelial neoplasia and prostatic carcinoma

A histochemical study of 27 well-differentiated prostatic carcinoma cases associated with prostatic intra-epithelial neoplasia (PIN) was carried out. In the histological areas examined a decreasing production of neutral mucin was found as follows: normal prostatic tissue (70%), prostatic carcinoma (55%), PIN 1 (50%), PIN 2 (30%) and PIN 3 (15%). A progressively increasing content of acidic mucin (AB 2.5) was observed in the areas of PIN 3 (25%), PIN 2 (35%) and prostatic carcinoma (70%), while it was absent in the areas of PIN 1 and normal prostatic tissue. Acidic mucin sulphated type (AB 1) was secreted only in PIN 3 (5%) and prostatic carcinoma (10%) areas. These data were correlated with the proliferative activity of PIN. It is postulated that the lower neutral mucin production by PIN 3 can be linked to the higher proliferative activity of this lesion. Moreover, the acidic mucin secretion by PIN and prostatic carcinoma is considered to be a further feature of these lesions.

Evaluation of three techniques for differential diagnosis of prostatic needle biopsy specimens

AIMS

To determine whether acidic mucin staining, lectin histochemistry using Wisteria floribunda agglutinin, and immunohistochemistry using the monoclonal antibody EAB 903 are of benefit in distinguishing between hyperplastic and carcinomatous prostatic glandular tissue in needle biopsy specimens.

METHODS

Formalin fixed, paraffin wax embedded prostatic needle biopsy specimens of benign and malignant tissue were examined. Alcian blue-periodic acid Schiff staining was performed on 33 benign and 34 malignant cases. Wisteria floribunda agglutinin (WFA) binding sites were demonstrated by the avidin-biotin peroxidase (ABC) technique with and without neuraminidase pretreatment on 34 benign cases and 32 malignant cases. EAB903 anticytokeratin antibody binding sites were demonstrated using both an indirect immunoperoxidase (IIP) technique and an avidin-biotin peroxidase complex method on seven benign and 31 malignant cases.

RESULTS

Acidic mucin staining was found in 17 of 34 malignant glands and was weakly positive in five of 33 benign glands. WFA positivity before neuraminidase pretreatment was present in 29 of 32 malignant glands and in 19 of 34 benign glands. After neuraminidase all benign and malignant cases showed positivity. EAB 903 positivity was seen in 11 of 31 malignant glands using the IIP technique and in two of 31 malignant glands using the ABC technique. In seven benign cases there was positivity in all glands using the IIP method with predominant basal cell staining in three and superficial cell staining in four. In benign cases using the ABC method two cases were negative.

CONCLUSIONS

None of the three methods studied showed sufficient sensitivity and specificity to allow their recommendation for routine diagnostic use.

Acidic mucin in the prostate: can it differentiate adenosis from adenocarcinoma?

Numerous reports have claimed that because acidic mucin is absent in benign prostatic glands and is present in some prostatic adenocarcinomas, this stain may be an adjunctive aid in the diagnosis of adenocarcinoma of the prostate. However, adenosis that mimics low-grade adenocarcinoma has not been evaluated to date. We studied 28 foci of adenosis for the presence of high iron diamine-alcian blue (HID-AB). Fifteen foci of adenosis (54%) showed strong staining for HID-AB; staining was diffuse in 11 cases and focal in four cases. An additional two cases (7%) showed equivocal staining. The remaining 11 cases (39%) lacked positivity. All cases of adenosis were verified with immunohistochemistry for keratin 903, a basal cell-specific antibody. This study demonstrates the limited use of acid mucin staining in the diagnosis of adenocarcinoma. The finding of HID-AB positivity in occasional isolated benign small prostatic glands within hyperplastic nodules suggests that acid mucin secretion may be a reflection of gland size or proliferation rather than evidence that adenosis is related to adenocarcinoma of the prostate.