Immunohistochemical analysis of clear cell carcinoma of the gynecologic tract

Carcinomas of ovary and lung with clear cell features: can immunohistochemistry help in differential diagnosis?

Metastatic lung carcinomas with clear cell morphology can be confused with primary ovarian clear cell carcinomas. We performed immunohistochemical stains in 14 cases of non-small cell lung carcinomas with clear cell features and 14 cases of ovarian clear cell carcinomas using a panel of markers, including thyroid transcription factor 1 (TTF-1), carcinoembryonic antigen (CEA), Wilms tumor gene 1, octamer-binding transcription factor 4 (OCT-4), cancer antigen 125 (CA-125), estrogen receptor, and progesterone receptor. Among non-small cell lung carcinomas with clear cell features, 87.5% of adenocarcinomas (or 50% overall frequency in lung carcinomas) were positive for TTF-1, whereas none of the ovarian clear cell carcinomas were positive (P = 0.002). All 14 ovarian clear cell carcinomas stained for CA-125 as compared with 1 non-small cell lung carcinoma (P < 0.001). On the other hand, 85% of non-small cell lung carcinomas stained for CEA, whereas none of the ovarian clear cell carcinomas did (P < 0.001). Interestingly, 4 ovarian clear cell carcinomas (28%) showed positive staining for the germ cell marker OCT-4. Either lung or ovarian carcinomas stained for Wilms tumor gene 1, estrogen receptor, or progesterone receptor very infrequently; and the difference between the 2 groups was not statistically significant. Our results suggest that an immunohistochemical panel consisting of TTF-1, CEA, CA-125, and OCT-4 is helpful in distinguishing most pulmonary and ovarian carcinomas with clear cell features.

Intraoperative cytology of clear cell carcinoma of the ovary

OBJECTIVE

To describe the cytomorphology of clear cell carcinoma (CCC) of the ovary in intraoperative samples of peritoneal fluid, imprint and scraping samples of the tumour tissue.

STUDY DESIGN

Fourteen histologically confirmed cases, stained by standard cytological procedures, were analysed by light microscopy.

RESULTS

In 33.3% of peritoneal fluid samples and 92.9% of imprint and scraping cytological samples, besides variable clear cell cellular morphology, one or both distinct cytological characteristics were observed: eosinophilic, hyaline, extracellular, globular substance with or without formation of a 'raspberry' body and an eosinophilic, intracytoplasmic inclusions. These structures were clearly seen only in samples stained by May-Grünwald-Giemsa.

CONCLUSION

Using cytological analysis of imprint and scraping samples of ovarian tumours it is possible to make a precise intraoperative cytological diagnosis in most cases of CCC of the ovary.

Urothelial carcinoma (clear cell variant) diagnosed with useful immunohistochemistry stain

The case is reported of urothelial carcinoma (clear cell variant) that was diagnosed with useful immunohistochemistry stain. A 70-year-old man, who had undergone left radical nephrectomy for renal cell carcinoma in August 2003 and partial lobectomy for pulmonary metastasis in May 2005, complained of hematuria in June 2005. On evaluation, a papillary pedunculated tumor was detected in the left wall of the urinary bladder. A transurethral resection of the bladder tumor (TUR-Bt) was performed in July 2005. The pathological diagnosis was difficult due to diffuse clear cell appearance. Immunohistochemistry stain showed urothelial carcinoma, not metastasis of the renal cell carcinoma. Finally it was diagnosed as urothelial carcinoma clear cell variant. Urothelial carcinoma has many variants that show a variety of appearances and characteristics. These should be well known before medical therapy is initiated.

Immunophenotypic diversity of endometrial adenocarcinomas: implications for differential diagnosis

Many endometrial adenocarcinomas, particularly those of endometrioid type, express estrogen receptors (ERs), progesterone receptors (PRs), and vimentin. This typical immunophenotype is frequently considered a standard against which others are compared when immunohistochemistry is used for differential diagnosis. We tested large numbers of endometrial cancers, enriched for high-grade tumors, to determine whether this reported immunophenotype was valid and whether expression differences between types of endometrial carcinoma could be exploited for diagnostic purposes. Immunohistochemical stains were performed on the following types of endometrial cancers using established methodology: International Federation of Gynecology and Obstetrics (FIGO) grades 1 and 2 endometrioid-42; FIGO grade 3 endometrioid-40; serous-24; clear cell-11; carcinosarcoma-9. In total, 92% of serous carcinomas expressed p16 strongly compared to weak-to-moderate expression of p16 in 7-67% of other tumors (FIGO grades 1 and 2 carcinoma and carcinosarcoma, respectively). A total of 84% of FIGO grades 1 and 2 carcinomas expressed ER compared to 9-54% of other tumors (clear cell and serous carcinomas respectively); 83% of FIGO grades 1 and 2 expressed PR compared to 11-54% of other carcinomas (carcinosarcoma and serous carcinoma, respectively). Most carcinomas were negative for monoclonal carcinoembryonic antigen (mCEA), and those that were positive showed mostly only focal membrane expression. Vimentin was expressed in nearly every tumor. Most tumors were diffusely vimentin positive, but a large range of expression patterns, from focal to diffuse and from weak to strong, was noted. Only 70% of FIGO grades 1 and 2 endometrioid carcinomas and 26% of grade 3 endometrioid carcinomas possessed the reportedly characteristic endometrial cancer immunophenotype p16 (-), ER (+), PR (+), mCEA (-), and vimentin (+). Endometrial cancers demonstrate substantial immunophenotypic diversity that remained apparent even within groups of similar histologic subtype and grade. ER, PR, and p16 expression was more illustrative of tumor type and degree of differentiation than they were of endometrial origin. In contrast, the vimentin-positive/CEA-negative phenotype remained the most constant among all endometrial cancers.

Clear cell adenocarcinoma of the endometrium is a biologically distinct entity from endometrioid adenocarcinoma

Clear cell adenocarcinoma (CCA) of the endometrium has a poor prognosis, although the biologic features of this rare tumor are not clear. In this study, we analyzed the expression of biologic markers relating to carcinogenesis, tumor growth, and progression. Thirteen cases of CCA were compared with cases of endometrioid adenocarcinoma (EMA) of the endometrium. Immunohistochemical staining for p53; Ki-67; cyclins A, D1, and E; E-cadherin; progesterone receptor (PR)-A and PR-B; P-glycoprotein; MLH1; and MSH2 was performed. Labeling indices of p53, Ki-67, and cyclins A, D1, and E in CCA were 46.4 +/- 24.3%, 52.1 +/- 20.5%, 37.9 +/- 21.4%, 12.3 +/- 27.9%, and 8.2 +/- 22.9%, respectively. E-cadherin was expressed in only 1 case (7.7%) of CCA, as compared to 39 cases (61.0%) of EMA. No CCAs were positive for PR-A and PR-B. P-glycoprotein was detected in seven cases (53.8%). Loss of either MLH1 or MSH2 expression occurred in eight cases (61.5%). High-level expression of p53, cyclin A, and P-glycoprotein, and low-level or no expression of cyclin E, E-cadherin, PR-A, and PR-B was observed in CCA compared with EMA. The mechanism of cell-cycle regulation in endometrial CCA is different from that in EMA and may influence its malignant potential. Endometrial CCA is a distinct entity from EMA.

Successful diagnosis of thromboembolism before surgery in a woman with clear cell adenocarcinoma of the endometrium

Patients with ovarian cancer with clear cell histology often have venous thromboembolism (VTE) even before surgery. In view of the possible association between clear cell histology and VTE in endometrial cancer, we measured the plasma levels of thrombin-antithrombin III complex (TAT) and D-dimer (DD) in the preoperative examinations of a patient with clear cell adenocarcinoma of the endometrium. Plasma TAT and DD were both highly elevated, though the patient had no symptoms of VTE or risk factors such as obesity or diabetes mellitus. Ultrasound Doppler examination and lung perfusion scintigraphy just before surgery revealed a thrombosis in the left popliteal vein and a pulmonary embolism. After implanting an inferior vena cava filter to prevent a fatal embolism of the lung, we performed abdominal total hysterectomy, bilateral salpingo-oophorectomy, and sampling of the pelvic lymph nodes. The VTE gradually disappeared and the plasma levels of TAT and DD returned to normal after surgery. Possibly, the VTE in this patient may have been associated with the clear cell histology.

Disappearance of steroid hormone dependency during malignant transformation of ovarian clear cell cancer

Ovarian clear-cell carcinoma (OCCA) and ovarian endometrioid carcinoma (OEMC) are often associated with endometriosis. This study determined the immunohistochemical expression of steroid hormone receptors and cancer-related genes in OCCA and OEMC specimens containing endometriosis and atypical endometriosis. Pathological progression from endometriosis to atypical endometriosis to carcinoma was identified in 4 of 22 OCCAs and 4 of 16 OEMCs. Using paraffin-embedded tissue samples, expression and changes in expression for estrogen receptors (ERs) and progesterone receptors (PRs) were examined in relation to the observed pathological changes. A gradual reduction in ERalpha and PRA expression was observed with malignant transformation from endometriosis to atypical endometriosis to OCCA. In OEMC, ERalpha expression increased with malignant transformation. In conclusion, reductions in ERalpha and PRA expression were observed with progression from endometriosis to atypical endometriosis in OCCA specimens. Disappearance of hormone dependency might therefore be associated with malignant transformation to OCCA.

Expression of CD10 and Cytokeratins in Ovarian and Renal Clear Cell Carcinoma

A solid pattern of tumor cells with a clear cytoplasm is common to both ovarian clear cell carcinoma (OvCCC) and renal clear cell carcinoma (RCCC). This study examined the possible differential expression of CD10 and cytokeratins (CK7, CK20, 34betaE12, and CAM5.2) between these two types. An immunohistochemical technique using peroxidase-labeled amino acid polymers was used to test formalin-fixed and paraffin-embedded tissues. In OvCCC, 6 of 29 cases were positive for CD10, and all cases had expression of CK7, 34betaE12, and CAM5.2. In contrast, all 24 RCCC cases had CD10 and CAM5.2 immunoreactivity, but none had any staining for 34betaE12. CK7 was only expressed in nine cases. No CK20 positivity was observed in any sample from either tumor type. Localization of CD10 expression was different in OvCCC versus RCCC. Although positive staining for 34betaE12 strongly suggests OvCCC, sometimes only a few cells may be stained. Therefore, 34betaE12-negative biopsies also should be evaluated for CD10 and CK7 immunoreactivity to enable histologic and cytologic differential diagnosis.

Yolk sac tumor of the vulva: a case report with long-term disease-free survival

BACKGROUND

Yolk sac tumor (YST) of the vulva is extremely rare. Seven cases of vulvar YST have been reported to the literature. Due to the rarity of tumors, the appropriate choice of treatment may remain unclear.

CASE

A 30-year-old woman presented with a 3.5-cm right labial mass. Excisional biopsy showed YST with predominant solid pattern. Three weeks after excision, right inguinal lymph node biopsy revealed metastatic tumor. The serum alpha-fetoprotein (AFP) was not elevated. Cisplatin-based chemotherapy was administered, followed by pelvic and groin irradiation. The patient was free of disease 90 months after the diagnosis.

CONCLUSION

Local excision of tumor with adjuvant cisplatin-based chemotherapy can be justified for vulvar YST. Inguinal lymphadenectomy is recommended because metastasis may occur early. Adjuvant radiation therapy may help to control the disease. Tumor size of 5 cm or less may be a favorable prognostic factor. Serum AFP level may not be a sensitive marker for follow-up of vulvar YST.

Clear cell adenocarcinoma of the tunica vaginalis of the testis with an adjacent uterus-like tissue

Testicular and paratesticular neoplasms that resemble the common epithelial type of ovarian tumor are quite rare. Paratesticular clear cell carcinoma is very uncommon in the testis, with no reported cases of a tumor arising from the tunica vaginalis in the literature to our knowledge. The present case shows that it is highly malignant and metastatic. The differential diagnosis of the tumor was made after thorough clinical, pathological and immunohistochemical investigations, from the mesothelioma of the tunica vaginalis, paratesticular serous papillary carcinoma, carcinoma of the rete testis, epididymal adenocarcioma, yolk sac tumor of the testis and metastatic carcinoma. The tumor showed Bcl-2 and Her-2/neu immunoreactivity, but was non-reactive for p53. This tumor, with a uterus-like structure as a paratesticular tumor-like mass, was composed of endometrial-type glands and stroma surrounded by bundles of smooth muscle, and is the third example of this kind of structure in English written literature. The patient, having normal external genitalia and fertility, represents the first reported case of paratesticular malignant differentiation of müllerian-type epithelium in the normal gonadal state. Müllerian-type epithelium located in the vicinity of the testis and/or endometriotic metaplasia of the mesothelium of the tunica vaginalis might be the possible origins for this uterus-like structure, and as a result, for this tumor.

Immunohistochemical staining for Ki-67 and p53 helps distinguish endometrial Arias-Stella reaction from high-grade carcinoma, including clear cell carcinoma

The distinction of the Arias-Stella reaction from clear cell carcinoma of the endometrium is usually straightforward; however, this differential diagnosis can be difficult when the Arias-Stella reaction occurs outside the setting of pregnancy or in older patients. The differential diagnosis also is problematic when serous or clear cell carcinoma focally arises within an endometrial polyp, as part of "endometrial intra-epithelial carcinoma" (EIC), or in younger patients. The goal of this study was to determine whether immunohistochemical staining can distinguish the Arias-Stella reaction from endometrial high-grade carcinoma, particularly clear cell carcinoma. Cases of endometrial Arias-Stella reaction (n = 27), clear cell carcinoma (n = 11), serous carcinoma (n = 7), and EIC (n = 4) were assessed by immunohistochemical staining with antibodies for Ki-67, p53, estrogen receptor (ER), and progesterone receptor (PR). Composite immunohistochemical scores based on the percentage and intensity of stained cells were calculated, as was the overall positivity (percentage positive cases), using a cutoff value of >/=5% stained cells and at least weak intensity. Appropriate statistical tests were performed. Ki-67 and p53 immunostaining was significantly less in Arias-Stella reaction than in clear cell carcinoma (p < 0.0001 for both) or serous carcinoma/EIC (p < 0.0001 for both), measured by the composite immunohistochemical scores or overall positivity. ER showed a significant difference only between Arias-Stella reaction and clear cell carcinoma; PR showed a significant difference only between Arias-Stella reaction and serous carcinoma/EIC. When clinical or histologic features cannot facilitate the differential diagnosis, immunohistochemical staining for Ki-67 and p53 may help distinguish endometrial Arias-Stella reaction from clear cell carcinoma and other types of high-grade carcinoma.

The Use of Cytokeratin 7 and EMA in Differentiating Ovarian Yolk Sac Tumors From Endometrioid and Clear Cell Carcinomas

Yolk sac tumors (YSTs) have a variety of morphologic patterns, some of which can resemble either endometrioid adenocarcinoma (EAC) or clear cell carcinoma (CCC). Immunohistochemical staining for alpha-fetoprotein (AFP) is usually only focal and thus is not always helpful in the diagnosis of YST, and pancytokeratin (CK) is expressed by all three tumors. We studied a battery of immunohistochemical markers with specific attention to the utility of cytokeratin 7 (CK7) in differentiating YST from EAC and CCC. A total of 46 ovarian tumors were retrieved for this study: 16 YST, 19 EAC, and 11 CCC. The three groups were analyzed for the expression of CK7, AFP, Leu-M1 (CD15), EMA, and WT1 by immunohistochemistry. In addition, CK and c-kit (CD117) were studied in the YSTs. All of the YSTs tested (100%) were positive for CK. CK7 was considered negative in all 16 YST cases (100%), although a few tumor cells (1%-2%) stained in 4 cases. In contrast, 17 of 19 EACs and all 11 CCCs had diffuse 3+ to 4+ positivity for CK7; the two other EACs showed 2+ positivity for CK7 (40% and 30% of the tumors). AFP was positive in 12 of 15 YSTs (80%), but was generally focal with 1+ staining in 10 cases (67%); only 2 cases were 3+. All of the EACs and CCCs were negative for AFP. Leu-M1 was 1+ in 9 of 15 YSTs (60%), while the remaining 6 were considered negative. Leu-M1 was positive in 10 of 15 EACs tested (67%), but the staining was variable with 1 case 3+, 3 cases 2+, and 6 cases 1+. In the CCCs, 10 cases (91%) were 3+ to 4+, and 1 case was 1+. EMA was essentially negative in 15 of 15 YSTs (100%), with 3 completely negative and 12 showing very focal (<5%) staining. Eight of 12 EACs showed 4+ staining, 3 showed 3+ staining, and 1 showed 2+ staining. All of the 11 CCCs (100%) showed 4+ staining. WT1 was negative in all cases of YST and CCC; 16 of 18 EAC tested (89%) were negative for WT1, but 2 (11%) were 4+ positive. C-kit was negative in all YSTs. In conclusion, it is important for pathologists to be aware that YSTs may mimic EACs and CCCs and that this distinction is important for the clinical management of patients with these tumors. AFP staining is focal in most YST, so an absence of staining does not exclude this diagnosis. CK7 and EMA are essentially negative in YST but are diffusely positive in CCC and EAC, making them useful markers for differentiating YSTs from both CCCs and EACs. Leu-M1 may also be helpful for distinguishing YSTs from CCCs.

Immunohistochemistry in gynaecological pathology: a review

This paper reviews some aspects of the application of immunohistochemistry in gynaecological pathology. The use of cytokeratins 7 and 20 are discussed with reference to applications in ovarian pathology, including metastatic disease to the ovaries. Developments in utilising MIB-1 and p16 in cervical squamous and glandular lesions are discussed. Recent assertions regarding the differential diagnosis between endocervical and endometrial carcinomas are also reviewed. Antibodies that may be of use in the diagnosis of uterine mesenchymal and ovarian tumours are highlighted, as are antibodies of use in trophoblastic lesions including the use of p57 in evaluating hydatidiform moles.

Skene's Gland Adenocarcinoma Resembling Prostatic Adenocarcinoma

An 88-year-old woman presented with gross hematuria and a 3-cm periurethral mass. Biopsy revealed an adenocarcinoma resembling prostatic adenocarcinoma; the tumor cells were positive for keratin and prostate-specific antigen. The serum level of prostate-specific antigen was elevated; the carcinoembryonic antigen and CA-125 serum levels were normal. One year after external beam radiotherapy, the patient is without evidence of disease. This is the sixth case of a urethral prostatic-type adenocarcinoma, tumors that are most likely of Skene's gland origin.

Ovarian yolk sac tumor associated with endometrioid carcinoma and mucinous cystadenoma of the ovary

The clinicopathologic and immunohistochemical findings of an unusual case of ovarian yolk sac tumor associated with endometrioid carcinoma and mucinous cystadenoma of the ovary are reported. The tumor was detected in a 51-year-old postmenopausal woman who presented with abdominal swelling and a pelvic mass. The patient underwent total abdominal hysterectomy with bilateral salpingo-oophorectomy and omentectomy. The tumor was confined to the right ovary and measured 16.0 cm in greatest dimension. Microscopic examination revealed that the tumor had a yolk sac component associated with an endometrioid carcinoma, grade I, and a mucinous cystadenoma. A background of atypical endometriosis was noted. Immunoperoxidase studies showed that the yolk sac component stained diffusely with a cytokeratin cocktail and was focally positive for alpha-fetoprotein. It was negative for keratin 7. In contrast, the endometrioid carcinoma stained positive for keratin 7 in addition to the cytokeratin cocktail, but was negative for alpha-fetoprotein. After surgery, the patient received three cycles of chemotherapy. However, the disease progressed and the patient died 10 months after the diagnosis of the ovarian tumor.

A panel of immunohistochemical stains assists in the distinction between ovarian and renal clear cell carcinoma

The diagnosis of primary clear cell carcinoma of the ovary or kidney is usually straightforward. However, problems in ascertaining the site of the primary tumor may arise when there is widespread metastatic disease or when clear cell carcinoma is present in both the ovary and kidney. In this study, the value of a panel of antibodies in distinguishing between an ovarian and renal clear cell carcinoma was evaluated. The panel comprised cytokeratin (CK)7 and 20, vimentin, estrogen receptor (ER), CD10, and renal cell carcinoma (RCC) marker. Ovarian clear cell carcinomas (n=14) were positive with CK7 (14/14), vimentin (6/14), ER (2/14), and RCC marker (2/14). All were negative with CD10 and CK20. Renal clear cell carcinomas (n=14) were positive with CD10 (14/14), RCC marker (14/14), vimentin (7/14), CK7 (2/14), and CK20 (1/14). All were negative with ER. This panel allows clear cell carcinomas of the ovary and kidney to be distinguished with a high degree of certainty and is a useful adjunct to histologic examination. Primary ovarian clear cell carcinomas are characterized by CK7 positivity, whereas primary renal neoplasms are characterized by positivity for CD10 and RCC marker and negative staining with CK7.

CD10 expression in epithelial tissues and tumors of the gynecologic tract: a useful marker in the diagnosis of mesonephric, trophoblastic, and clear cell tumors

We tested 417 cases of formalin-fixed, paraffin-embedded normal or hyperplastic gynecologic tissues as well as neoplasms involving the gynecologic tract with a monoclonal antibody against CD10 (clone 56C6), with special emphasis on epithelial and epithelial-like structures and tumors. CD10 was always expressed in mesonephric remnants (mesonephric remnants of the uterine cervix, epoophoron, rete ovarii) and tumors (mesonephric adenocarcinoma of the uterine cervix, tumors of wolffian origin of the broad ligament and ovary). CD10 was also positive in the syncytiotrophoblast, cytotrophoblast, and intermediate trophoblast of normal gestations, partial and complete moles, choriocarcinoma, and placental site trophoblastic tumors. Finally, CD10 was positive in several metastatic neoplasms to the gynecologic tract (100% in metastatic renal clear cell and intestinal carcinomas and melanomas). In contrast, CD10 was almost invariably negative in müllerian epithelia of the female genital tract and in their corresponding tumors, with the exception of focal expression found in squamous epithelia and tumors with squamous differentiation. Thus, the expression of CD10 may be useful in the establishing the diagnosis of mesonephric and trophoblastic tumors and in the differential diagnosis between gynecologic clear cell carcinoma (always negative) and metastatic clear cell carcinoma of renal origin.

Clear cell carcinoma of the urinary bladder: a report and comparison of four tumors of mullerian origin and nine of probable urothelial origin with discussion of histogenesis and diagnostic problems

Carcinomas of the bladder that resemble clear cell carcinoma of mullerian type are rare. Whether such neoplasms 1) arise from mullerian elements in the bladder and are histogenetically identical to the female genital tract cancer, 2) are a peculiar variant of vesical adenocarcinoma of nonmullerian derivation, or 3) represent a peculiar morphologic expression of transitional cell (urothelial) carcinoma with gland differentiation is often uncertain. We reviewed the clinical, conventional pathologic, and immunohistochemical features of 13 neoplasms with exclusive, or predominant, morphologic features of clear cell carcinoma. The 11 female and two male patients were 22-83 (mean 57) years of age. The clinical and gross features had no unique aspects. On microscopic examination the most common pattern, present in all cases, was tubulocystic, with a papillary pattern, present in six tumors and a predominant solid growth in one. Cells with abundant clear cytoplasm were conspicuous in nine tumors and hobnail cells were seen in eight. Four tumors showed focally recognizable patterns of transitional cell (urothelial) carcinoma in the available material. In five other tumors pseudostratified epithelium reminiscent of transitional epithelium was present focally. Endometriosis was present in two cases. In two other cases benign cysts focally lined by ciliated epithelium and surrounded by elastosis were interpreted as most likely mullerian. Immunohistochemistry was performed in 10 cases. All tumors stained for CA 125 (usually strong, ranging from focal to diffuse) and nine tumors stained for CK7 (usually strong and diffuse). CK20 was focally and weakly positive in four tumors and extensively positive in another. The same immunohistochemical panel was performed on 10 typical transitional cell carcinomas, 4 transitional cell carcinomas with gland differentiation, not otherwise specified, and 5 pure adenocarcinomas of the bladder (one of urachal origin). Minimal CA 125 positivity was seen in two transitional cell carcinomas. CA 125 staining was seen in the areas of gland differentiation in three of four transitional cell carcinomas and three of five pure adenocarcinomas but was focal in most cases. All transitional cell carcinomas and transitional cell carcinomas with gland differentiation showed extensive CK7 positivity. In contrast, only one of four positive pure adenocarcinomas showed >5% CK7-positive cells. Although all groups showed CK20 positivity, the percentage of CK20 positive cells was higher in pure adenocarcinomas. Prostate specific antigen was negative in all tumors. The cytokeratin immunoprofile of clear cell carcinomas of the bladder is closer to transitional cell carcinomas and transitional cell carcinomas with gland differentiation than pure adenocarcinomas arguing against an unusual form of adenocarcinoma. Our finding of CA 125 expression in bladder tumors of apparent urothelial origin contrasts with some studies that have regarded CA 125 expression as evidence for a mullerian origin. The frequency of gland differentiation in transitional cell carcinomas and the rarity of vesical endometriosis could be taken to suggest that these tumors are mostly of urothelial derivation, but the strong female preponderance in our series argues for a mullerian origin in at least some cases, and this is almost certain in the four cases with benign mullerian components. In the absence of endometriosis or conventional foci of transitional cell carcinoma, it may be impossible to determine whether a tumor with the morphology of clear cell carcinoma is of mullerian or transitional (urothelial) cell lineage, and at this time immunochemistry does not solve this problem.