IntrOductIOnBreast lumps are common in women of all ages. A thorough examination of breast is very important to rule out Breast cancer since it is the most common cancer in women. WHO estimates, more than half a million deaths worldwide are due to Breast cancer [1]. Recently, Breast cancer has overtaken cervical cancer in India with the incidence rate being 26 per 100,000 women population and mortality rate of 13 per 100,000 women population [2]. With the advent of triple testing for breast malignancies, FNAB has become an integral part of the evaluation of breast lesions. Triple testing includes breast clinical examination, mammography and/or ultrasonography, and cytology {FNAB/Core needle biopsy (CNB)} [3].FNAB is a simple, relatively painless, inexpensive OPD procedure with speedy results. One of the major goals of Breast FNAB is to differentiate benign from malignant lesions. Differentiation is not possible in all cases due to significant overlap of the cytomorphologic features of both benign and malignant breast lesions [4]. To address these cytomorphologic grey zone uncertainties and to bring a degree of uniformity to the reporting system, in 1996 the National Cancer Institute (NCI) proposed five diagnostic categories [5]. Since then use of FNAC in the evaluation of breast lesions has changed substantially over the period of 20 years, mainly due to changes in screening programs and available treatments and recent preference for CNB.In 2016, the International Academy of Cytology (IAC) established a "Breast Group" which included pathologists, radiologists, surgeons, and oncologists mainly to produce comprehensive and standardised guidelines for breast FNAB cytology reporting. The IAC Yokohama System for Reporting Breast Cytopathology incorporates the indications for breast FNAB cytology, FNAB technique, smear making and material handling, a reproducible standardised reporting system, the use of ancillary diagnostic and prognostic tests, and correlation with clinical work-up algorithms. Ultimately, this will facilitate clinician's understanding and use of FNAB cytology in breast pathology [6].In the Yokohama System for Reporting Breast Cytopathology, the "Breast Group" has proposed a five-category classification: category 1insufficient material; category 2-benign; category 3-atypical, probably benign; category 4-suspicious for malignancy, probably in situ or invasive carcinoma; and category 5-malignant [6]. In the present study, the newly proposed IAC Yokohama system of breast FNAB cytology was applied to breast FNAB cytology cases from the Pathology Department and ROM of each category and the diagnostic yield of this technique calculated. This categorisation of the Breast FNAB cytology according to IAC Yokohama system of reporting helps pathologist in the diagnostic clarity and guides clinician in the appropriate patient management, hence the need for this study. The main objectives of the study were to categorise the Breast FNAB samples according to this new system of reporting and to assess the ROM for each...