Under parous (p) and nulliparous (np) conditions, median time to tumor formation (MTTF) was similar for both ErbB2 (p = 214 and np = 244 days) and ErbB2/IRS2 bigenic mice (p = 211 and np = 264 days) (Fig. 1a and b). Here, IRS2 is linked to neoplasm.