Epidermal growth factor receptor (EGFR) downstream molecules as response predictive markers for gefitinib (Iressa®, ZD1839) in chemotherapy‐resistant non‐small cell lung cancer

Gefitinib has shown meaningful antitumor activity with tolerable toxicity in chemotherapy-refractory NSCLC in previous studies. Moreover, EGFR expression failed to show a correlation with response. In an attempt to identify predictive markers of response, we have investigated the tumoral expression of key signaling molecules of EGFR (EGFR, p-EGFR, p-Akt, p-Erk, p-STAT3) by immunohistochemistry and analyzed their correlations with response. Of 65 patients who received gefitinib (250 mg/day) for chemotherapy-refractory NSCLC, there were 14 partial responses (21.5%), 21 stable diseases (32.3%) and 21 progressive diseases (32.3%). Median durations of overall survival and time to progression were 6.7 months and 2.8 months, respectively. Immunohistochemistry was performed in 34 patients with evaluable tissue specimens. EGFR was overexpressed (2+ or 3+) in 32.4% and p-EGFR was positive in 26.5%. The expressions of p-Akt, p-Erk and p-STAT3 were positive (1+ or 2+) in 50%, 38.2% and 79.4%, respectively. The EGFR expression was not correlated with p-EGFR or the downstream molecules. EGFR or p-EGFR status did not correlate with response. Positive expression of p-Erk was significantly associated with poor response (38.1% in -, 14.3% in 1+, 0% in 2+; p = 0.046). Furthermore, tumors with positive p-Akt and negative p-Erk nuclear expression exhibited the best response (60%), whereas there was no response in the opposite p-Akt (-), p-Erk (+) cases. Intense nuclear staining of p-Akt (2+) was associated with prolonged TTP (HR 0.25, 95% confidence interval CI 0.08-0.79, p = 0.018) and OS (HR 0.16, 95% CI 0.04-0.62, p = 0.008). These results support the assumption that gefitinib responsiveness might be predicted by activated EGFR downstream molecules such as p-Akt and p-Erk.