• High cohesive, uniform small cells in two-dimensional flat honeycomb sheets;
• Cytoplasm usually delicate and scant without secretory mucin vacuoles;
• Round to oval nuclei, <2 RBCs, with smooth nuclear membrane and fine, even chromatin;
• Nucleolus, inconspicuous and single;
• Few single benign cells may be present with intact cytoplasm;
• Mild to moderate atypia may be present within limits in benign proliferative conditions.

• Oval to elongated nuclei with smooth outlines, about the size of one RBC;
• Chromatin is fine, even and hyperchromatic without nucleoli;
• Naked epithelial nuclei: larger and rounder;
• Naked stromal nuclei: larger and more spindle, may have nucleoli.

• Cohesive, regular flat sheets. Occasional papillary groups.
• Benign single cells are common;
• Abundant, dense and finely granular cytoplasm with distinct cell border. Blue-gray to purple in Diff-Quick and blue to bright orange in Pap;
• Fairly uniform eccentric nuclei with smooth nuclear membrane;
• Finely granular and evenly dispersed chromatin with one single round prominent nucleoli;
• Benign apocrine cells may show markedly atypia that mimic malignant cells. However, they are rare with a spectrum from benign to the most atypical apocrine cells in a reactive background.

• Acute inflammation, debris, granulation tissue, macrophage or multinucleated giant cells, and fat necrosis;
• Epithelial and stromal cells may display reactive atypia.

• Large, foamy macrophages, multinucleated giant cells,  blood pigment;
• Acute or chronic inflammation, granuloma tissue and fibrotic tissue;
• Reactive macrophage and fibroblasts may show high atypia

• Many mild to moderate crowded cohesive sheets;
• Relatively uniform epithelial cells with benign features;
• Presence of myoepithelial cells

• Crowded multilayered glands or microacini formed by small ductal cells;
• Naked bipolar nuclei.

Reference

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