HER2 expression (HR 0.25, 95% CI 0.1–0.7) was associated with a decreased risk for pneumonitis; the highest risk of pneumonitis was seen in those who had 1 + expression by immunohistochemistry (IHC), when compared to 3 + expression (HR 6.0, 95% 1.6–22). The gene discussed is ERBB2; the disease is pneumonitis.