1. Oncology: Discontinue T-DM1. Of note, it is reasonable to cautiously continue T-DM1 in selected patients with mild HPS. If disease stable, or no evidence of disease, consider observing off systemic therapy. Otherwise, prescribe alternative HER2-targeted therapy with no or minimal risk of liver or pulmonary toxicity.2. Cardio-Pulmonary: Prescribe supplemental oxygen, as needed. Exclude other causes of hypoxemia.3. Hepatology: No specific measures other than treat cause. Hold T-DM1 and minimize exposure to other hepatotoxic agents, if possible. The gene discussed is ERBB2; the disease is Hermansky-Pudlak syndrome.