Inhibin-like material--an immunohistologic marker for prostatic origin of metastases.

Immunocytochemical localization of inhibin-like material (ILM) using a specific antiserum generated against ILM of prostatic origin was carried out in metastatic lymph nodes of known primary prostatic tumours and in rectal biopsies showing direct invasion with known prostatic carcinoma. Nine of the 11 metastatic lymph nodes gave positive reaction, which was readily apparent in differentiated tumours showing micro-acinar formation. In poorly differentiated tumours it was often focal and indicated intracytoplasmic staining within randomly scattered cells. Rectal biopsies showing invasion of prostatic carcinoma (4 cases) also showed positive reaction for ILM. Using this experimental protocol, the reaction for metastatic lesions from patients with non-prostatic carcinomas was completely negative indicating the specificity of the test for prostatic origin of metastasis. In conclusion, the present investigation indicates the potential application of ILM in confirming or excluding the prostatic origin of invasive tumour in metastatic lesions.