Cetuximab is a monoclonal antibody that targets the human epidermal growth factor receptor (EGFR). Although approved for use in EGFR-overexpressing advanced colorectal cancer, recent studies have shown a lack of association between EGFR overexpression and cetuximab response, requiring the identification of novel biomarkers predictive of response to this agent. To do so, 22 colon cancer cell lines were screened for cetuximab response in vitro and sensitive and resistant lines were identified. In sensitive cell lines, cetuximab induced a G 0 -G 1 arrest without inducing apoptosis. Notably, cetuximabsensitive but not cetuximab-resistant cell lines were preferentially responsive to EGF-stimulated growth. Whereas neither EGFR protein/mRNA expression nor gene copy number correlated with cetuximab response, examination of the mutation status of signaling components downstream of EGFR showed that cell lines with activating PIK3CA mutations or loss of PTEN expression (PTEN null) were more resistant to cetuximab than PIK3CA wild type (WT)/PTENexpressing cell lines (14 F 5.0% versus 38.5 F 6.4% growth inhibition, mean F SE; P = 0.008). Consistently, PIK3CA mutant isogenic HCT116 cells showed increased resistance to cetuximab compared with PIK3CA WT controls. Furthermore, cell lines that were PIK3CA mutant/PTEN null and Ras/BRAF mutant were highly resistant to cetuximab compared with those without dual mutations/PTEN loss (10.8 F 4.3% versus 38.8 F 5.9% growth inhibition, respectively; P = 0.002), indicating that constitutive and simultaneous activation of the Ras and PIK3CA pathways confers maximal resistance to this agent. A priori screening of colon tumors for PTEN expression status and PIK3CA and Ras/BRAF mutation status could help stratify patients likely to benefit from this therapy.

Obesity is common in women and is associated with a number of adverse health outcomes including cardiovascular disease, infectious diseases, and cancer. We explore the relationship between obesity and immune cell counts in women in a longitudinal study of 322 women from 1999 through 2003 enrolled as HIV-negative comparators in the Women's Interagency HIV Study. Body mass index (BMI, kg/m(2)) was categorized as normal weight (BMI 18.5-24.9), overweight (BMI 25-29.9), obese (BMI 30-34.9), and morbidly obese (BMI >/=35). CD4 and CD8 counts and percents and total lymphocyte and white blood cell (WBC) counts were measured annually using standardized techniques. A mixed model repeated measures analysis was performed using an autoregressive correlation matrix. At the index visit, 61% of women were African American; mean age was 35 years, and median BMI was 29 kg/m(2). Immunologic parameters were in the reference range (median CD4 count, 995 cells/mm(3); CD8 count, 488 cells/mm(3); total lymphocyte count, 206 cells/mm(3); median WBC, 6 x 10(3) cells/mm(3)). In multivariate analyses, being overweight, obese, or morbidly obese were independently associated with higher CD4, total lymphocyte, and WBC counts than being normal weight; morbid obesity was associated with a higher CD8 count. The strongest associations between body weight and immune cell counts were demonstrated in the morbidly obese. Increasing body weight is associated with higher CD4, CD8, total lymphocyte, and WBC counts in women. Investigation into the impact of obesity on immune function and long-term adverse outcomes is needed.

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