The Use of the International Academy of Cytology Yokohama System for Reporting Breast Fine-Needle Aspiration Biopsy

A Systematic Review and Meta-analysis

Ilias P. Nikas, MD; Johannes A. Vey, MSc; Tanja Proctor; Mousa M. AlRawashdeh; Angela Ishak, MD; Hyang Mi Ko, MD, PhD; Han Suk Ryu, MD, PhD


Am J Clin Pathol. 2023;159(2):138-145. 

In This Article

Abstract and Introduction


Objectives: To perform the first meta-analysis regarding the pooled risk of malignancy (ROM) of each category of the Yokohama system for reporting breast fine-needle aspiration, as well as assess the latter's diagnostic accuracy using this new system.

Methods: Two databases were searched, followed by data extraction, study quality assessment, and statistical analysis.

Results: The "Insufficient" "Benign" "Atypical" "Suspicious" and "Malignant" Yokohama system categories were associated with a pooled ROM of 17% (95% CI, 10%-28%), 1% (95% CI, 1%-3%), 20% (95% CI, 17%-23%), 86% (95% CI, 79%-92%), and 100% (95% CI, 99%-100%), respectively. When both "Suspicious" and "Malignant" interpretations were regarded as cytologically positive, sensitivity (SN) was 91% (95% CI, 87.6%-93.5%) and false-positive rate (FPR) was 2.33% (95% CI, 1.30–4.14%). A summary receiver operating characteristic curve was constructed and the pooled area under the curve was 97.3%, while the pooled diagnostic odds ratio was 564 (95% CI, 264–1,206), indicating a high level of diagnostic accuracy. When only "Malignant" interpretations were regarded as cytologically positive, the pooled FPR was lower (0.75%; 95% CI, .39%-1.42%) but at the expense of SN (76.61%; 95% CI, 70.05%-82.10%).

Conclusions: Despite Yokohama's system early success, more data would be needed to unravel the system's value in clinical practice.


Breast cancer has become the most common cancer worldwide, while it ranks fifth in the cancer mortality list, according to the latest GLOBOCAN estimates.[1] Breast fine-needle aspiration (FNA) is a safe, minimally invasive, accurate, and cost-effective modality to assess palpable and nonpalpable breast lesions, which is best interpreted in correlation with the other components of the "triple test" (clinical examination and radiology), in a multidisciplinary context.[2–5] However, it has largely been replaced by core-needle biopsy (CNB), especially in the setting of breast cancer screening programs.[3,6,7] As a result, many laboratories have reduced the use of FNA only for specific applications—for instance, while evaluating cystic lesions or when the clinical suspicion of cancer is low.[6,8]

The International Academy of Cytology (IAC) Yokohama system for reporting breast FNA biopsy has been recently developed, having the goal to standardize reporting and improve communication among physicians.[2,3] The system contains five reporting categories—"Insufficient" "Benign" "Atypical" "Suspicious" and "Malignant"[2,3]—each linked with a specific risk of malignancy (ROM) and a selection of management recommendations.[2,3] As no meta-analysis has been performed so far regarding this new system, our study aimed to

  1. Calculate the pooled ROM of each reporting category of the Yokohama system

  2. Assess the diagnostic accuracy of breast FNA to detect malignancy, using the Yokohama system