An Open-Label Study to Characterize the Incidence and Severity of Diarrhea in Patients With Early-Stage HER2+ Breast Cancer Treated With Neratinib and Loperamide

This is an open-label, Phase 2 study that will investigate the incidence and severity of diarrhea in early-stage HER2+ breast cancer patients receiving neratinib with loperamide, alone and in combination with an anti-inflammatory treatment or a bile acid sequestrant treatment, or neratinib dose escalation, who have previously undergone a course of trastuzumab therapy in the adjuvant setting. Patients will receive: * Neratinib 240 mg orally once daily with food for thirteen 28-day cycles. * Loperamide daily for two 28-day cycles and then as needed. * Amendment 3, an anti-inflammatory treatment for one cycle and loperamide to be administered daily for two 28-day cycles and then as needed. Closed to enrollment. * Amendment 4, colestipol for one cycle and loperamide to be administered one cycle and then as needed. Closed to enrollment. * Amendment 5, colestipol for one cycle and loperamide as needed. Closed to enrollment. * Amendment 6/6.1, 120 mg neratinib for Week 1 (C1D1-C1D7), followed by 160 mg neratinib for Week 2 (C1D8-C1D14), followed by 240 mg neratinib for Week 3 and thereafter (C1D15 to end of treatment). Loperamide as needed. Closed to enrollment. * Amendment 7/7.1, 160 mg neratinib for the first 2 weeks (C1D1 - C1D14), followed by 200 mg neratinib for the next 2 weeks (C1D15 - C1D28), followed by 240 mg neratinib thereafter (C2D1 to end of treatment). Loperamide as needed.