Background: Obesity has been associated with worse pathological complete response (pCR) to neoadjuvant chemotherapy (NACT) and overall outcome in breast cancer patients (pts). Our aim was to retrospectively evaluate body mass index (BMI) as a predictive factor of pCR to NACT in pts treated at our institution, taking into account tumor HER2 status and CT dose adjustment. Pts and methods: Pts with invasive breast cancer who received NACT followed by surgery at Vall d'Hebron University Hospital from January 2004 to December 2008 were analyzed. Pts were categorized as normal/underweight (BMI < 25 kg/m2), overweight (BMI of 25 to < 30 kg/m2), and obese (BMI ≥30 kg/m2). The overweight and obese groups were combined (BMI-high) and then compared with the normal/underweight group. Univariate and multivariate analyses were performed to assess the association between BMI and pCR (no invasive tumor in breast and nodes). Results: 256 consecutive pts were included. Median age was 52.5 years. According to BMI, 38.7% were normal/underweight and 59.4% were BMI-high. 23.4% of the pts had HER2 positive tumors (n=60), 84% received anthracyclines-and taxanes-based CT, and 46.6% of the HER2 positive pts were treated with trastuzumab. Drug dose was reduced in only five pts with a body surface area > 2m2. No statistically significant association was found between BMI and any tumor characteristics. In the univariate analysis, BMI-high was associated with worse pCR in the whole population (p=0.017), as well as in HER2 positive pts (p=0.013). In the multivariate analysis, BMI did not significantly predict pCR in the total population, although a trend was observed (p=0.098). In the HER2 positive subgroup, however, BMI was an independent predictive factor of pCR (p=0.001). Among luminal A [estrogen receptor positive and/or progesterone receptor positive and (Ki67 < 20% and histological grade 1 or 2)], luminal B [estrogen receptor positive and/or progesterone receptor positive and (Ki67 ≥20% or histological grade 3)], and triple negative tumors, BMI was not a predictive factor of pCR. Conclusions: Our results suggest that higher BMI is likely associated with worse pCR, particularly in HER2 positive pts. A better understanding of the molecular links between obesity and breast cancer is necessary to identify new predictive factors of pCR to NACT. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P4-03-04.

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