• Abundant epithelial cells: ductal type, cohesive orderly regular honeycomb sheets, antler-like papillary fronds; small to moderate delicate cytoplasm with indistinct cell borders; relatively round to oval nuclei with fine, evenly distributed chromatin and smooth nuclear membranes; nuclei may be moderately enlarged (<2RBCs) with moderate pleomorphism and prominent nucleoli; Intact individual benign epithelial cells are present;

• Abundant naked oval nuclei: Myoepithelial cells origin-small, dark, naked bipolar nuclei with inconspicuous nucleoli; Stromal origin-larger, more open chromatin and prominent nucleoli;

• Stromal fragments: clearly demarcated fibromyxoid material, spindle cells, no fat or inflammation;

• Fibroadenoma may show high cellularity and high atypia. Features suggestive of a benign diagnosis: focal atypical changes with a spectrum from very benign to high atypia; stromal fragments; antler-like clusters, honeycomb sheets; fine chromatin, smooth nuclear membrane; apocrine metaplasia; lactational changes; naked bipolar nuclei;

• Epithelial variants of fibroadenoma: florid hyperplasia, cellular fibroadenoma;

• Differential Diagnosis of Fibroadenoma and Fibrocystic Disease

  	Fibroadenoma	Fibrocystic Disease
  Clinical	Round, single, unilateral, mobile	Ill-define mass, bilateral, multiple
  Epithelium	Abundant	Less abundant
  Pattern	larger antler sheets	Smaller sheets
  Naked oval nuclei	More	Less
  Stromal fragments	Prominent	less or none
  Background	Maybe myxoid	Maybe cystic

Reference

• The art and science of cytopathology. Richard M Demay, MD. 1996