Stromal infiltration as a predictor of tumor invasion in breast fine-needle aspiration biopsy

Clinical management of in situ carcinoma of the breast is different from invasive carcinomas. Thus, it is important to find cytomorphologic criteria to distinguish between these two entities. The current study is designed to assess whether, by applying strict cytologic criteria, the status of stromal invasion can be predicted. In this retrospective study, 223 consecutive nonpalpable tumors sampled by ultrasound-guided breast fine-needle aspirates with diagnosis of in situ and invasive carcinoma with histologic follow-up evaluation were retrieved. Ten cytologic parameters were evaluated, which included cellular clustering, eosinophilic differentiation, necrosis, tubular structures, dirty background, nuclear anisonucleosis, cellular pleomorphism, cribriform pattern, tubular structures, and stromal infiltration. Among all the parameters examined, stromal infiltration was the most powerful predictor of status of invasion. Stromal infiltration was significantly higher in invasive (88%) than in situ (11%), P < 0.0001. In contrast, cribriform pattern (16% vs 36%) and necrosis (19% vs 59%) were more frequently seen in situ than in invasive carcinomas with P-values of 0.0008 and <0.0001, respectively. This study demonstrates that stromal infiltration defined by strict criteria may predict the status of tumor invasion in breast fine-needle aspirates. The combination of stromal infiltration and cribriform pattern and necrosis in aspirates may provide an opportunity in introducing a "predictive index" to differentiate between an in situ versus an invasive process.