Collision tumour in the pelvic cavity: rectal leiomyosarcoma and prostate adenocarcinoma

We report a rare and, to our knowledge, as yet undescribed type of collisio n tumour - rectal leiomyosarcoma and prostate adenocarcinoma. Our study als o provides the first data on molecular alterations [polymerase chain reacti on/loss of heterozygosity (LOH) analysis] of the APC, NF-1, DCC, p53, nm23- H1 and BRCA-1 genes in the two components of the collision tumour. None of the genes examined in this study expressed LOH in the prostate carcinoma co mponent of the collision tumour. By contrast, in the leiomyosarcoma compone nt, LOH was found at the DCC and p53 genes, proving that these two tumours did not arise from the same stem cell but represent two different neoplasti c growths.