Monoclonal development of squamous cell carcinomas from polyclonal papillary or nodular hyperplasias in the forestomach of C3H/HeN↔BALB/c chimeric mice treated with N-methyl-N-nitrosourea or diethylnitrosamine

The clonality of epithelial proliferative lesions of forestomach carcinogenesis was immunohistochemically investigated in C3H/HeN↔BALB/c chimeric mice using a specific antibody to C3H strain specific antigen (CSA) and as well as in terms of microsatellite DNA polymorphism patterns. The C3H/HeN↔BALB/c chimeric mice were produced by an aggregation procedure. Male chimeric, C3H/HeN, and BALB/c animals were given N-methyl-N-nitrosourea (MNU) 0.5 mg/mouse once a week for a total of 10 times by intragastric intubation or 30 p.p.m. diethylnitrosamine (DEN) in their drinking water for 20 weeks. Those treated with MNU were killed at weeks 11, 25 and 45 and with DEN at week 35. Normal chimeric forestomach epithelium was found to demonstrate mixtures of epithelial cell groups composed of either CSA positive or negative cells. The same was the case for all simple hyperplasias. Papillary and nodular (PN) hyperplasias increased with time even after cessation of MNU treatment and many of them consisted of both CSA positive and negative cell groups. In one case, a CSA positive and a negative cancer were observed to have developed independently in the same PN-hyperplasia consisting of both parental cell types. In 28 tumor bearing chimeric mice, all squamous cell carcinomas (SCCs) were composed entirely of either CSA positive or negative tumor cells. However, in two animals with advanced CSA positive cancers and negative cancers, tiny cancer nests composed of both parental type cells were found in association. Microsatellite DNA polymorphism patterns of DNAs sampled from histological sections completely conformed with the outcomes of immunohistochemical staining. The results suggest that PN-hyperplasias are aggregates (polyclonal) of preneoplastic changes from which monoclonal SCCs are derived. Polyclonal cancers may also arise secondarily at low incidence during progression, due to two or more lesions coalescing.