Purpose: Data from two large phase III studies were analyzed to characterize the correlation between the occurrence of rash during treatment with the epidermal growth factor receptor inhibitor erlotinib and improved clinical outcomes.

Experimental Design: Overall survival, progression-free survival (PFS), and tumor response were compared between patients in a rash-evaluable subset who did or did not develop rash in National Cancer Institute of Canada Clinical Trials Group Studies BR.21 (single agent in non–small-cell lung cancer, n = 444 in erlotinib group and n = 229 in placebo group) and PA.3 (combination with gemcitabine in pancreatic cancer, n = 254 in erlotinib plus gemcitabine group and n = 245 in placebo plus gemcitabine group).

Results: Presence of rash strongly correlated with overall survival in both studies. In Study BR.21, these correlations increased with rash severity grade: grade 1 versus no rash [hazard ratio (HR), 0.41, P < 0.001] and grade ≥2 versus no rash (HR, 0.29, P < 0.001). Similar results were observed for PFS. Disease control (complete response + partial response + stable disease) seemed to increase with the presence and severity of rash. In Study PA.3, grade ≥2 rash (but not grade 1) strongly correlated with overall survival improvement: grade ≥2 versus no rash (HR, 0.47, P < 0.001). Similarly, grade ≥2 rash was strongly correlated with improvements in PFS and disease control.

Conclusions: Physicians and patients should view rash development as a positive event indicative of greater likelihood of clinical benefit. Further studies are required to identify patients most likely to develop rash and to determine if dose escalation to induce rash can improve efficacy.