Clinically relevant tumors with complete or almost complete absence of MUC5AC staining included small cell carcinoma of the lung (0% of 17), papillary thyroid carcinoma (0% of 359), breast cancer (2% of 1097), prostate cancer (2% of 228), soft tissue tumors (0.1% of 968), hematological neoplasias (0% of 111), and clear cell renal cell carcinoma (0% of 507). The gene discussed is MUC5AC; the disease is breast cancer.