Recently, a study examined the value of ‘pathological reactive stroma’ (defined as stromal-predominant breast cancer) as a predictor for trastuzumab resistance in patients with early HER2-positive breast cancer receiving adjuvant therapy in the FinHER phase III trial, reporting an association between trastuzumab resistance and the presence of ‘reactive stroma’ [79]. The gene discussed is ERBB2; the disease is breast cancer.