Adenoid Cystic Carcinoma
Less than 0.1% of mammary carcinomas have an adenoid cystic growth pattern. The term cylindroma, previously used interchangeably with adenoid cystic carcinoma, refers to the histologic appearance that suggests entwined cylinders of stroma and epithelial cells. Adenoid cystic carcinoma occurs in adult women throughout the age distribution of mammary carcinoma, with patients between ages 25 and 80 and a reported mean age that varies from 50 to 63 years. Isolated cases have been encountered in men and in children (1,2). No predilection exists for adenoid cystic carcinoma to develop bilaterally, but other types of carcinoma may occur in the contralateral breast (3,4), or, in rare instances, another carcinoma may be found elsewhere in the same breast (5).
Adenoid cystic carcinoma usually presents as a discrete firm mass. Calcifications can form in these tumors, leading to detection by mammography, but, in some instances, the mammogram was reportedly negative (4). The typical mammographic image is that of a lobulated mass (6). In one case, the tumor presented as an 8-mm hypoechoic nodule suggestive of an intramammary lymph node before periodic mammographic follow-up revealed increasing density and less discrete margins (7). Pain or tenderness has been described in a minority of cases. The median duration of a symptomatic mass in one series was 24 months (4). Most adenoid cystic carcinomas have been described as hormone receptor-negative by biochemical and immunohistochemical analysis with occasional tumors positive for estrogen and/or progesterone receptors at relatively low levels (8,9,10).
Gross size of the lesions varies from 2 mm to 12 cm, with the majority between 1 and 3 cm. Low-grade tumors tend to be smaller (mean 1.6 cm) than high-grade tumors (mean 3.5 cm). Many adenoid cystic carcinomas are circumscribed or nodular grossly, but the majority have an invasive growth pattern microscopically (Fig. 17.1). Microcystic areas formed by the coalescent spaces in dilated glands are found in some tumors.
Adenoid cystic carcinoma consists of a mixture of proliferating glands (adenoid component) and stromal or basement membrane elements (“pseudoglandular” or cylindromatous component). These elements are usually not distributed homogeneously in a given tumor (Fig. 17.2). Some regions may consist only of the adenoid elements that are indistinguishable from cribriform carcinoma (11). Abundant stromal material in other parts of the tumor can produce a pattern that can be mistaken for scirrhous carcinoma. Because of this intratumoral heterogeneity, adenoid cystic carcinoma may be difficult to recognize in a needle core biopsy specimen if a characteristic sample has not been obtained (Figs. 17.2, 17.3). Inspissated secretion and stromal fragments from benign lesions or other forms of carcinoma may be mistaken for cylindromatous material in needle core biopsy samples.
The microscopic growth patterns of mammary adenoid cystic carcinoma have been described as cribriform, solid, glandular (tubular), reticular (trabecular), and basaloid. Focal sebaceous and adenosquamous differentiation are variably present (4). Adenomyoepitheliomatous and syringomatous areas are further evidence of structural diversity. Perineural invasion is found in a minority of mammary tumors, and lymphatic tumor emboli are extremely uncommon (Fig. 17.4). Shrinkage artifacts, a relatively frequent occurrence in histologic sections of adenoid cystic carcinoma, may be mistaken for lymphatic tumor emboli.