Pseudoinvasion in intraductal carcinoma.

: Fine-needle aspiration, stereotactic biopsies, and guide wire localization have introduced an element of pre-excision trauma to mammary lesions. Dislodgement of tumor cells may result in diagnostic difficulties and misinterpretation of a tissue artifact as an invasive carcinoma. Eight breast biopsy specimens with intraductal carcinoma (ranging from cribriform to comedo types) displayed changes suggestive of an invasive carcinoma. Three of the patients had a prior history of needle aspiration; the remaining five women had undergone needle localization to guide the biopsy. In all cases, two or more dislodged tumor cell clusters were found in the stroma or adipose tissue either immediately adjacent to a disrupted duct with intraductal carcinoma or in the nearby stroma. Those cases with prior needle aspiration were associated with significant hemorrhage and reactive changes with small, rounded clusters of tumor cells within pools of blood. The needle localization specimens had minimal tissue reaction with larger fragments of detached cell clusters. Breast trauma by a puncturing instrument (needle or guide wire) can disrupt mammary ducts with intraductal carcinoma and dislodge the proliferating cells into the surrounding stroma. The dislodged cells simulate invasion. To minimize damage to the architectural integrity of the lesion under investigation, limits should be imposed on the number of needle passes.