Despite national guidelines, the evaluation of effects of primary systemic treatment (PST) in breast cancer is a complex challenge. Our aims were to evaluate the response patterns focusing on correlations of radiological and pathological tumor size, regression heterogeneity in different molecular subtypes, cellularity changes and the incidence of enlarged, multinucleated neoplastic cells related to therapy. Slides of pretreatment biopsies and resection specimens of consecutive cases were reevaluated focusing on heterogeneity of regression per whole slide, and 40x or 100x magnification fields. Alteration in cellularity and the presence of multinucleated tumor giant cells were noted. The correlation of pathological and radiological sizes and their alterations were analyzed by Spearman rank correlation. The present study included 106 tumors. A decrease in size (84.9%) and cellularity (76.4%) was noted in all molecular subtypes. Inhomogeneous regression was found in 45.3%, with minor inhomogeneity in the majority. Scatter pattern regression was seen only in 8 cases (7.5%). Significant correlations were found between the pathological and radiological sizes (p = 0.02), and between the alterations of cellularity and pathological and radiological size (p = 0.04; p = 0.03, respectively). Multinucleated tumor giant cells were noted in 17.9% (n = 19), nearly exclusively in cases treated with PST including taxanes. Regression inhomogeneity following PST is present in about half of the cases, and is not related to molecular subtypes. The evaluation of the maximum area of the tumor bed is recommended for the proper evaluation of regression. Multinucleated tumor giant cells are related to PST including taxane derivate, and may cause upgrading.
Keywords: Breast cancer; Molecular subtypes; Primary systemic therapy; Regression pattern.