Criterion

Benign

Malignant

General characteristics

Cellularity

Usually poor or moderate

Usually high

Cell to cell cohesion

Good with large defined clusters of cells

Poor with cell separation resulting in dissociated cells with cytoplasm or small groups of cells

Cell arrangement

Even, usually in flat sheets (monolayer)

Irregular with overlapping and three-dimensional arrangement

Cell types

Mixtures of epithelial, myoepithelial and other cells with fragments of stroma

Usually uniform cell population

Bipolar (elliptical) naked nuclei

Present, often in high numbers

Not conspicuous

Background

Generally clean except in inflammatory conditions

Occasionally with necrotic debris and sometimes inflammatory cells including macrophages

Nuclear characteristics

Size (in relation to red blood cell (RBC) diameter)

Small

Variable, often large, depending on tumour type

Pleomorphism

Rare

Common

Nuclear membranes (Pap stain)

Smooth

Irregular with indentations

Nucleoli (Pap stain)

Indistinct or small and single

Variable but may be prominent, large and multiple

Chromatin (Pap stain)

Smooth or fine

Clumped and may be irregular

Additional features

Apocrine metaplasia, foamy macrophages

Mucin, intracytoplasmic lumina

(Modified from: GUIDELINES FOR NON-OPERATIVE DIAGNOSTIC PROCEDURES AND REPORTING IN BREAST CANCER SCREENING.  NHSBSP Publication No 50 June 2001).