Small cell carcinoma of the urinary bladder is a rare and aggressive
tumor resembling
small cell carcinoma of the lung.
Thyroid transcription factor 1 (TTF-1) expression is common in
small cell carcinomas arising in the lung. However, studies of its expression in extrapulmonary
small cell carcinomas have yielded varying results. Because information concerning the immunohistochemical profile of
small cell carcinoma of the urinary bladder is limited, we investigated the immunoreactivity of this
tumor to a battery of
antibodies in a series of 44 cases. Using 5-mum sections cut from
paraffin-embedded tissue blocks, immunohistochemistry was performed to detect TTF-1,
cytokeratin (CK) 7, CK20, and
uroplakin antigenicity in 44 cases of
small cell carcinoma of the urinary bladder. None of the patients had primary lung
tumors. The TTF-1 immunohistochemical
stain showed nuclear positivity in 17 cases (39%). Positive immunostaining for CK7 was observed in 26 cases (59%). There was no positive staining with either CK20 or
uroplakin. There was no correlation between TTF-1 expression and survival (P = .27). In addition, TTF-1 expression did not correlate with clinicopathological characteristics, including age (P = .74), sex (P = .53), smoking history (P = .96), clinical stage (P = .10), pathological T stage (P = .50),
lymph node metastasis (P = .40), and distant
metastasis (P = .58). In summary, TTF-1 expression in
small cell carcinoma of the urinary bladder was found in 39% of the
tumors, demonstrating that this marker is expressed in
small cell carcinomas other than those of pulmonary origin.
Small cell carcinoma of the urinary bladder is positive for CK7 immunostaining in 59% of cases consistent with its origin from urothelium. Unlike urothelial
carcinoma, expression of CK20 and
uroplakin in
small cell carcinoma of the urinary bladder is consistently negative, and thus, these stains do not appear to be useful in the diagnosis of this
neoplasm. TTF-1 positivity is not a significant prognostic factor in
small cell carcinoma of the urinary bladder.