Breast morphological changes with the menstrual cycle

(A) Stage 1 of menstrual cycle. Low magnification of lobule showing acini clustered with barely perceptible epithelial and myoepithelial layer. Nuclei are round to oval with basophilic cytoplasm and sparse stromal infiltrate, with occasional sprinkling of mast cells seen. Eosinophilic secretions are noted within the lumina. Higher magnification of lobule showing the uniform lack of vacuolation.

(B) Stage 2 of menstrual cycle. Low magnification of lobule showing appearance of vacuolation in the myoepithelial layer with prominent distinction between the two layers of the acini. High magnification of lobule showing increasing tendency for basal vacuolation.

(C) Stage 3 of menstrual cycle. Low magnification of lobule showing prominent myoepithelial vacuolation with edema of the stroma. The eosinophilic secretions within the lumina are present. High magnification of the acini showing prominent vacuolation.

(D) Stage 4 of menstrual cycle. Low magnification of lobule showing extensive stromal edema and infiltrate with myoepithelial vacuolization. High magnification of the acini showing prominent mitotic figure and apoptotic body in the epithelial layer.