Quantitative examination of mechanophysical tumor cell enrichment in fine-needle aspiration specimens

BACKGROUND. The advent of cDNA microarrays and other molecular technologies necessitates the acquisition of tumor cell-enriched material because nonmalignant cells often decrease the sensitivity of the assays. Fine-needle aspiration (FNA) specimens from carcinoma have long been noted to be enriched in malignant cells. The current study quantitated the relative representation of tumor versus nontumor cells in FNA specimens compared with tissue sections using breast carcinoma as a model. METHODS. Five patients who had undergone both a diagnostic FNA and a surgical excision for breast carcinoma between January and July of 1996 were selected. Five random cellular fields from representative slides of the FNA (using the ThinPrep preparation of the wash) and surgical excision specimens were photographed digitally at ×20 power. The cells were judged as tumor or nontumor cells and then were counted manually in each field. RESULTS. The calculated percentage of malignant cells in the FNA specimen (as represented on the ThinPrep slide) ranged from 66-93% compared with the calculated percentage of 37-78% noted in histologic sections. The average of all 5 fields from all 5 cases showed that 83.1% of the total cells were malignant in the ThinPrep preparation compared with 62.3% in the histologic sections. This difference was highly statistically significant when analyzed using the chi-square test (P = 0.0009). CONCLUSIONS. The percentage of malignant cells on FNA specimens from breast carcinoma, as assessed by ThinPrep, was found to be significantly higher than that obtained by surgical excision. The results of the current study quantitatively confirm the impression of practicing cytopathologists, but also suggest that FNA will provide a good substrate for cDNA microarray and other molecular analyses.