15065 Background: Pmab is a fully human mAb against EGFr approved by the US FDA for treating pts with mCRC who have disease progression on or following regimen based on fluoropyrimidine, oxaliplatin, and irinotecan. Due to the important role of the EGFr in skin growth, cutaneous reactions are common adverse events of Pmab, mainly an acneiform follicular eruption. Other skin toxicities of Pmab include hypertrichosis and trichomegaly. The mechanism behind the EGFr-induced hair growth is poorly understood. This study attempted to find patterns distinguishing the group of pts that developed hypertrichosis from the group of pts which did not. Methods: The dermatological manifestations of 24 pts on four clinical studies were noted. When comparing skin toxicities of the pts, the worst severity grade developed while on study was used. Hypertrichosis is defined as excessive hair growth growing in places that do not normally have hair and not induced by androgens. Trichomegaly is defined as excessive growth of the eyelashes. Pts were separated into a group that developed hypertrichosis and a group that did not, with further delineation according to gender, race and therapy (tx) regimen. Results: 41.6% of pts developed hypertrichosis or trichomegaly in a median 3.46 months after the first dose of Pmab. The majority of pts developed hair growth on the cheeks, upper lip, chin; two pts had periobital and three had chest hair growth. No statistically significant differences were noted in gender, race, or median age of pts with and without hypertrichosis. There is no correlation between hypertrichosis and severity of the other skin toxicities, monotx or combination tx, or presence of anti-tumor response. Patterns of hair growth and histologic features will be presented. Conclusions: Pmab may alter the growth cycle of the hair follicle in both men and women. The characteristic trichomegaly and hypertrichosis are related to duration of tx and show no relationship to the other skin toxicities. A higher response rate was observed in pts with hypertrichosis, but this is related to the duration of anti-tumor tx. Further studies are needed to characterize the etiology and mechanism of this cutaneous toxicity. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Amgen Amgen, Genentech, Pfizer, sanofi-aventis