Table 3.

Selective pressure against wild-type p53 in doxycycline-independent tumors

		p53 status of primary tumor
		No LOH	LOH	Total
p53 status of	No LOH	6 (33%)	0 (0%)	6 (33%)
doxycycline-	LOH	8 (44%)	4 (22%)	12 (67%)
independent  secondary  tumor	Total	14 (78%)	4 (22%)	18 (100%)

Primary mammary tumors occurring in doxycycline-treated MTB/TWNT/p53(+/−) mice frequently gave rise to secondary doxycycline-independent tumors following withdrawal of inducer. Shown is a contingency table derived from analysis of 18 primary-secondary tumor pairs. Southern analysis was performed on genomic DNA derived from each tumor to determine whether selective loss of the wild-type p53 allele (LOH) had occurred. Eight of 18 tumor pairs were discordant for p53 LOH, and in all eight discordant pairs, p53 LOH was identified in the secondary tumor. Doxycycline-independent tumors were significantly associated with selective loss of wild-type p53 (p < 0.025, McNemar's test).