Garcia-Casado et al. BMC Cancer 2010, 10:36 http://www.biomedcentral.com/1471-2407/10/36 Deviations of genotype frequencies from those expected under Hardy-Weinberg equilibrium (HWE) were assessed by c2 (p > 0.05) tests [33]. To study the impact of the biological factors on progres- sion-free survival (PFS), the Kaplan-Meier proportional risk test (Log Rank) was used [34,35]. PFS was defined as the time interval from the start of treatment to local or distant disease progression. Those patients that reported disease progression during the follow-up were considered as censored, being the data of confirmation of this pro- gression considered in the calculation of PFS. Univariate predictors of PFS were entered into a Cox proportional hazards model using stepwise selection to identify the independent predictors of poor outcome, a confidence interval (CI) of 95% was also considered [36]. Results Patient and tumor characteristics Ninety-five stage II-III ER/PgR-positive BC in postme- nopausal women treated with letrozole as neoadjuvant therapy were analyzed. The median age of the series was 78.3 years (range: 61.7-89.8). The histopathological and clinical characteristics of the series are summarized in Table 1. As shown, 67 patients presented infiltrating ductal carcinoma (IDC), 16 infiltrating lobular carci- noma (ILC) and the remaining 12 cases corresponded to 9 mucinous carcinomas, 2 tubular carcinomas and one medullar carcinoma. The histological grade was available in only 52 of the IDC due to sample limitations. Most of the cases were stage IIa BC (68.4%), the majority of cases having a T2 tumor (80%). All tumors expressed HR (ER or PgR or both). Considering the whole HR expression for each patient we distinguished two groups of cases: those having low level HR (expressing HR in ≤ 40% of tumor cells) and those with a high HR expres- sion (> 40% of cells). Ten cases were classified in the first group (10.5%). HER2 and Ki67 expression was also evaluated, 32 cases were HER2 ++/+++ (33.7%) and 32 out of 73 cases analyzed expressed Ki67 (44.4%). The median treatment period with letrozole as neoad- juvant therapy was 10.23 months (range: 3.53-85). Response to treatment was evaluated by radiological means (mammogram or ultrasound) at four months of letrozole administration using WHO criteria [37]. A total of 34 partial responses (PR) and one complete response (CR) where achieved, and were classified as responders for the analysis. Hence, the overall radiologi- cal response rate at 4 months (RR4M) was 36.8%. On the contrary, 55 women remained with stable disease (SD) and 5 developed progression disease (PD), these all being considered as non-responders. Page 4 of 11 Table 1 Clinical and pathological characteristics of the patients. Parameter Histological diagnosis* IDC ILC Others Histological grade I II III Tumor size (T) T2 T3-T4 Lymph node involvement (N) N0 N1-2 Stage IIa IIb IIIa-IIIb ER PgR HR** HER2 Negative 10-40% 40-70% > 70% Negative 10-40% 40-70% > 70% ≤ 40% > 40% Negative + ++ +++ Ki67 Negative Positive Response to letrozole Non responders Responders Progression status No progression Progression n (%) 67 (70.5) 16 (16.8) 12 (12.6) 29 (55.8) 19 (36.5) 4 (7.7) 76 (80.0) 19 (20.0) 76 (80.0) 19 (20.0) 65 (68.4) 20 (21.1) 10 (10.5) 5 (5.3) 8 (8.4) 25 (26.3) 57 (60.0) 28 (29.5) 18 (18.9) 24 (25.3) 25 (26.3) 10 (10.5) 85 (89.5) 39 (41.1) 24 (25.3) 22 (23.2) 10 (10.5) 40 (55.6) 32 (44.4) 60 (63.2) 35 (36.8) 77 (81.1) 18 (18.9)