The genetic background modifies the spontaneous and X-ray-induced tumor spectrum in the Apc 1638N mouse model

The effect of the genetic background on the tumor spectrum of Apc1638N, a m ouse model for attenuated familial adenomatous polyposis (FAP), has been in vestigated in X-irradiated and untreated F1 hybrids between C57BL/6J1co-Apc 1638N (B6) and A/JCrIBR (A/J), BALB/cByJIco (C) or C3H/HeOuJIco (C3). Simil ar to the Apc(Min) model, the Apc1638N intestinal tumor multiplicity seems to be modulated by Mom1. Moreover, several additional (X-ray-responsive) mo difier loci appear also to affect the Apc1638N intestinal tumor number. The genetic background did not significantly influence the number of spontaneo us desmoids and cutaneous cysts in Apc1638N. In general, X-irradiation incr eased the desmoid multiplicity in Apc1638N females but had no effect in mal es. The opposite was noted for the cyst multiplicity after X-rays. Surprisi ngly, X-irradiated CB6F1-Apc1638N females were highly susceptible to the de velopment of ovarian tumors, which displayed clear loss of the wild-type Ap c allele. Genes Chromosomes Cancer 24: 191-198, 1999. (C) 1999 Wiley-Liss, Inc.