The objective of this study was to introduce the clinical and cytological aspects of myospherulosis. A total of 5,174 consecutive breast fine needle aspiration (FNA) cytology cases were reviewed, among which 23 cases of myospherulosis of the breast were found, all in female patients. The main findings of myospherulosis, best seen with the Papanicolaou stain, consisted in the observation of spherules that were homogeneously smooth or contained one or more internal dense bodies. Routine Papanicolaou-stained slides with or without Romanowsky staining were analyzed. Immunocytochemistry was conducted for carbonic anhydrase 1 (CA1), glycophorin C, KP1, and PGM1. The patients' ages ranged from 41 to 79 years (mean age: 56 years). Of the 23 patients, 21 had a previous history of breast surgery. Cytologically malignant or suspicious diagnoses were made in four of the 23 cases. The size of parent bodies varied from 18.2 to 151 μm (mean, 52 μm). The size of spherules ranged from 2.1 to 16.4 μm (mean, 6.6 μm). Immunocytochemistry showed that the myospherules reacted with anti-CA1 and anti-glycophorin C antibodies. Most breast myospheruloses occur in patients with a history of breast surgery. Immunocytochemistry for CA1 and glycophorin C can enhance the diagnosis of myospherulosis.
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