# Identifying Micropapillary Patterns With Fine-Needle Aspiration Biopsy at Metastatic Sites to Enhance Breast Cancer Diagnosis: A Case Series

## TL;DR

This case series explores using fine-needle aspiration biopsy to identify micropapillary breast cancer patterns in metastatic sites, improving diagnosis and treatment guidance.

## Contribution

The study demonstrates the utility of FNAB in detecting micropapillary carcinoma features in metastases, aiding in the diagnosis of this aggressive breast cancer subtype.

## Key findings

- FNAB revealed angulated, avascular clusters and reversed polarity in metastatic samples, consistent with IMPC features.
- Higher cellularity and atypia in FNAB correlated with a greater proportion of IMPC in primary tumors.
- FNAB is a rapid, minimally invasive method for assessing metastases and guiding clinical decisions.

## Abstract

Invasive micropapillary carcinoma (IMPC) of the breast is a rare and aggressive subtype of invasive breast carcinoma, distinguished by its unique morphological characteristics. This case series analyzes fine-needle aspiration biopsy (FNAB) specimens obtained from metastatic sites in suspected breast cancer patients between 2022 and 2024, integrating detailed clinical, histopathological, and immunohistochemical information. Six samples (four axillary lymph nodes, two skin nodules) from four patients (three females, one male; mean age 60) were analyzed. Cytological examination revealed variability in cellularity and grade, as well as the presence of angulated, avascular papillaroid and morule/cell ball-like clusters with reversed cellular polarity and variable background mucin. Notably, increased cellularity, atypia, and distinct cytological patterns at metastatic sites on FNAB, coupled with reduced background mucin, showed a strong correlation with a higher proportion of IMPC in the corresponding primary breast tumors. FNAB emerges as a rapid, minimally invasive, and cost-effective technique for assessing peripheral metastases, aiding not only in the detection of this rare and aggressive subtype but also in guiding clinical management by providing valuable insight into its extent within the primary tumor.