Breast Fine Needle Aspiration Biopsy Cytology Using the Newly Proposed IAC Yokohama System for Reporting Breast Cytopathology: The Experience of a Single Institution.

Objective: Recently the International Academy of Cytology (IAC) proposed a new reporting system for breast fine needle aspiration biopsy (FNAB) cytology. We aimed to categorize our samples according to this classification and to assess the risk of malignancy (ROM) for each category as well as the diagnostic yield of breast FNAB.

Study Design: Breast FNAB specimens obtained between January 2007 and December 2017 were reclassified according to the newly proposed IAC Yokohama reporting system. The ROM for each category was determined. Diagnostic yield was evaluated based on a three-category approach, benign versus malignant.

Results: The samples were distributed as follows: insufficient material 5.77%, benign 73.38%, atypical 13.74%, suspicious for malignancy 1.57%, and malignant 5.54%. Of the 3,625 cases collected, 776 (21.4%) had corresponding histology. The respective ROM for each category was 4.8% for category 1 (insufficient material), 1.4% for category 2 (benign), 13% for category 3 (atypical), 97.1% for category 4 (suspicious for malignancy), and 100% for category 5 (malignant). When only malignant cases were considered positive tests, the sensitivity, specificity, and diagnostic accuracy were 97.56, 100, and 99.11%, respectively.

Conclusions: Our study is the first to categorize breast FNAB cytology samples according to the proposed IAC reporting system and to evaluate patient outcomes based on this categorization.