THE ORIGIN AND BIOLOGY OF CIS CELLS - GENERAL DISCUSSION

Participants at the 4th Copenhagen Workshop on Carcinoma in situ and C ancer of the Testis, representing cell biologists and tumour biologist s, met together to discuss the similarities and differences between pr imordial germ cells (PGCs) of the embryo, and the carcinoma in situ (C IS) stem cell of human testicular germ cell tumours (GCTs). Much has b een discovered about PGCs in the last 10 years and we still do not kno w the exact nature of CIS cells. Knowledge of PGCs comes mainly from m ouse experiments and knowledge of CIS comes from the study of human tu mours. A mouse model of human GCT would help to investigate the nature of CIS cells. Grafting mouse male genital ridges into mouse fetal tes tes results in the development of testicular tissue and the formation of teratomatous tumour components. Amplification of PGCs in culture is possible but this results in their transformation into embryonic germ (EG) cells. CIS cells die by apoptosis if they are isolated, and shor t-term culture is only possible if the CIS cells are cultured in their normal environment within seminiferous tubules. It may be possible fo r CIS cells to differentiate in culture although they cannot be mainta ined in culture as isolated cells. Human CIS cells are likely to be fo rmed as a result of in utero factors rather than agents acting on norm al adult testicular germ cells. EG cells stimulate feeder cells by par acrine factors but it is not known if these cells produce autocrine fa ctors.