When these Stat5a−/− mice were bred to MMTV-tva mice, infected with RCAS-caErbb2, impregnated 4 days post infection, and analyzed at I10, the resultant early lesions exhibited significantly lower levels of pSTAT5 than did the lesions in Stat5a+/+ mice (Figure 5A) confirming the predominance of STAT5a in the mammary gland. The gene discussed is STAT5A; the disease is infection.