Prostate cancer with small-cell morphology: an immunophenotypic subdivision.

OBJECTIVE: To study the immunophenotypic characteristics and clinical outcome of morphologically undifferentiated prostatic carcinoma with small-cell morphology (U-PC-SCM).

MATERIAL AND METHODS: Sixteen patients with U-PC-SCM were enrolled. The streptavidin-biotin complex immunohistochemical method was used on paraffin-embedded tissue sections to test positivity for prostate-specific antigen, prostate-specific acid phosphatase, CD57, androgen receptors, CK8-18, epithelial membrane antigen, carcinoembryonic antigen, CD56, neuron-specific enolase, chromogranin, synaptophysin, serotonin, various hormones, thyroid transcriptional factor-1 and Ki-67/MIB1.

RESULTS: Based on immunophenotypic criteria, we identified two groups of patients. The final diagnosis was U-PC (Gleason score 10) in Group 1 (n=9) and pure or mixed neuroendocrine small-cell carcinoma in Group 2 (n=7). Group 1 underwent total androgen blockade (TAB) with no major response and had a median survival of 9 months. In Group 2, three patients underwent TAB, two of whom died of progressive disease. The third patient showed a partial response (PR) for 18 months but eventually relapsed with liver metastatic lesions. He was then treated with cisplatin + etoposide and showed a PR for 3 months and survived for 5 months after the initiation of the second-line chemotherapy (CTH) treatment. The other four patients received six cycles of cisplatin + etoposide. There were two complete responses of >14 and >22 months, respectively and 2 PRs of 11 and 17 months, respectively, the partial responders surviving for 14 and 21 months, respectively.

CONCLUSION: U-PC-SCM with a neuroendocrine immunophenotype is a histogenetically distinct entity with different clinical and laboratory manifestations which responds well to a cisplatin + etoposide CTH regimen.