Figure 2. RANK controls the incidence and onset of progestin-driven mammary cancer.

a, Carcinogenesis scheme involving MPA and DMBA. Nulliparous six-week-old female mice were implanted subcutaneously with MPA pellets and treated orally with DMBA as indicated for eight weeks. b, Onset of palpable mammary tumours in MMTV-Cre rank^floxed/Δ females (RANK^Δmam) (n = 14) and age-matched littermate control females (n = 19) treated with MPA pellets and DMBA as indicated in a. Data are shown as the percentage of tumour-free mice after the last DMBA challenge. Median tumour onset for controls was 11 days after the last DMBA treatment; for RANK^Δmam females it was 30 days. c, Representative histological sections of mammary tumours isolated from control littermate and RANK^Δmam females 22 days after the last DMBA treatment. Cytokeratin 5 staining is shown. Original magnifications ×20. d, e, Numbers of carcinomas in situ and invasive mammary cancers in control and RANK^Δmam females on day 7 (d) and day 22 (e) after the final DMBA treatment. Data are shown as means±s.e.m. per mouse (n = 3 mice per genotype). All ten mammary glands were analysed for each mouse. Asterisk, P < 0.05 (Student’s t-test). Bottom panels show representative histological sections with typical invasive adenocarcinomas in the control females. For RANK^Δmam females, normal acinar morphology (day 7) and a carcinoma in situ (day 22) are shown. Haematoxylin/eosin (H&E)-stained sections and immunostaining for the proliferation marker Ki67 are shown. Original magnifications ×20.