THE SPECTRUM OF THE GRAY-ZONE IN BREAST CYTOLOGY - A REVIEW OF 186 CASES OF ATYPICAL AND SUSPICIOUS CYTOLOGY

A ''gray zone'' exists in fine needle aspiration (FNA) cytology of bre ast; there an unequivocal diagnosis cannot be made. Previous studies h ave reported a gray zone incidence of 6.9-20%. We reviewed 2,197 fine needle aspirations (FNAs) of the breast performed at our institution t o determine the incidence of the gray zone, analyze the sources of dif ficulty and establish guidelines to minimize the size of the gray zone . One hundred eighty-six (10%) of the total 2,197 FNAs were diagnosed as atypical (91) or suspicious for malignancy (95). The cytologic smea rs from all 186 equivocal cases and histopathologic sections from 156 of these patients who underwent a biopsy or mastectomy were reviewed. Clinical follow-up was obtained on the remaining 30 cases. Upon review , the causes of the equivocal diagnoses were divided into three catego ries: (1) technical, in which the smears were either markedly limited in cellularity or obscured by blood and/or drying artifact; (2) inexpe rience, which included cases that were reclassified by the reviewing c ytopathologist as benign or malignant; and (3) the overlap of cytologi c features of benign and malignant lesions due to the nature of the le sion, justifying a confirmational biopsy. Technical difficulties accou nted for 103 equivocal diagnoses (4.5%); inexperience of the cytopatho logist was responsible for 44 cases (2.4%). The third category, which represents the true gray zone in breast cytology, accounted for 39 cas es (2%). Fibroadenomas constituted the largest single cause of equivoc al diagnoses (27 cases). These fibroadenomas exhibited very cellular s mears with marked discohesiveness and occasional nuclear atypia and pr ominent nucleoli. Other bl east lesions in this category were intracys tic papillary carcinoma, low grade apocrine carcinoma, solitary intrad uctal papilloma, and intraductal and atypical hyperplasia. The remaini ng lesions, and useful criteria of help with the differential diagnosi s of the above categories, are discussed.