64P Mammographic density to predict response to neoadjuvant chemotherapy for breast cancer

Abstract

Mammographic density (MD) has been strongly associated with increased risk of breast cancer (BC). In view of this, we aimed to investigate the predictive value of MD in a large consecutive cohort of BC patients (pts) treated with neoadjuvant chemotherapy (NAC). Data on NAC treated pts prospectively collected in the registry of Fondazione IRCCS Istituto Nazionale dei Tumori, Milan (May 2009-Aprill 2020) were identified. Diagnostic mammograms were used to evaluate MD, which was categorized by the Breast Imaging-Reporting and Data System (BI-RADS). BI-RADS identify 4 categories of MD in keeping with the masking effect of fibroglandular tissue, as following: A (almost entirely fat), B (scattered areas of fibroglandular density), C (heterogeneously dense), and D (extremely dense). Multivariable logistic regression was used to assess the odds ratios (OR) for pathological complete response (pCR), ie absence of invasive tumor in breast and node surgical specimens, comparing BI-RADS categories with adjustment for patient age, BMI, and tumor characteristics. A total of 442 pts were analyzed, of which 120 (27.1%) attained a pCR. BI-RADS categories A, B, C, and D accounted for 10.0%, 37.8%, 37.1% and 15.2% of cases, respectively, with corresponding pCR rates of 20.5%, 26.9%, 30.5%, 23.9%. At multivariable analysis cases classified as BI-RADS C showed an increased likelihood of pCR as compared to A (odds ratio [OR]=2.79), B (OR=1.70), and D (OR=1.47) independently of age, BMI (OR underweight vs normal=3.76), clinical N and T (OR T1/Tx vs T4=3.87), molecular subtype (HER2 vs luminal=10.74; triple negative vs luminal=8.19). In subgroup analyses, the strongest association of MD with pCR was observed in triple negative (ORs of B, C and D versus A: 1.85, 2.49 and 1.55, respectively) and HER2 positive cases (ORs 2.70, 3.23, and 1.16). Notably, no significant differential effect of MD with respect to pCR was observed in luminal BC (ORs of B, C and D versus A: 0.88, 2.01 and 1.58). Patients with dense breast are more likely to attain a pCR after NAC at net of other current clinical and pathological predictive factors. The potential of MD to assist decisions on BC management and as a stratification factor in neoadjuvant clinical trials should be considered.