Mammary analogue secretory carcinoma (MASC) usually consists of multiple lobules separated by fibrotic stroma. The lobules display a variety of architectural patterns, including solid, microcystic, macrocystic, papillary, tubular and cribriform (shown here). Multiple patterns may be seen within one tumor. The tumor cells have bland morphology with uniform round to oval vesicular nuclei and small nucleoli. The cytoplasm is pale eosinophilic and granular or vacuolated. High-grade cytologic features and increased mitotic activity are usually not present.