Table 1.

λ cII mutant frequencies in mammary glands and tumors

Mouse ID	Age (months)	Mammary glands			Mammary tumors
		Total pfu × 103	Mutant plaques	Mutant frequency × 10−5	Total pfu × 103	Mutant plaques	Mutant frequency × 10−5
neu-1	19	381	56	14.7	280	98	35.0
neu-2	19	274	42	15.3	188	72	38.3
neu-3	20	220	60	27.3	288	123	42.7
neu-4	20				263	63	24.0
neu-5	23	272	54	19.8	285	98	34.4
neu-6	23				178	82	46.1
neu-7	17				184	25	13.6
neu-8	23	233	50	21.7	164	180	31.7
neu-9	24	223	38	17.0	192	56	29.2
neu-10	25				234	42	18.0
neu-11	25	102	21	20.7	443	64	14.4
Mean ± SEM				19.5 ± 2.1			29.8 ± 3.3
wt-1	6.0	144	21	14.6
wt-2	4.5	523	98	18.7
wt-3	4.0	220	29	13.2
wt-4	4.0	243	26	10.7
wt-5	5.5	157	17	10.8
wt-6	4.0	148	19	12.8
wt-7	5.5	142	18	12.7
Mean ± SEM				13.4 ± 1.0

Tissues are derived from: (neu-1 through neu-11) ErbB2/Big Blue bitransgenic mice carrying both the MMTV-c-erbB2 transgene and a second transgene consisting of multiple copies of the λ bacteriophage genome; or (wt-1 through wt-7) phenotypically wild-type Big Blue single transgenic mice crossed once to FVB/N mice. Note that although the wild-type group was substantially younger than the bitransgenic group, contralateral “normal” mammary tissues from seven tumor-bearing ErbB2/Big Blue bitransgenic mice were subjected to cII mutation analyses and their collective mutant frequency was significantly lower than the frank tumors (P < 0.05).