Microsecretory Adenocarcinoma of Salivary Glands.

Salivary gland classification has benefitted immensely from the growing field of molecular diagnostics. Microsecretory adenocarcinoma, a novel salivary gland malignancy recently included in the fifth edition of the World Health Organization Classifications of Head and Neck Tumours, is one such example. This novel entity was discovered among the umbrella category of adenocarcinoma, not otherwise specified, using a combination of careful histologic analysis and advanced molecular techniques. Its strikingly characteristic histologic features including subtle infiltration, flattened tubules, and abundant blue secretions highlight the necessity of meticulous morphologic observation, even in the age of increased molecular testing. It harbors a recurrent novel MEF2C::SS18 gene fusion, which is amenable to fluorescence in situ hybridization analysis. It presents predominantly in the oral cavity with a propensity for the palate and the majority are thus far low grade, clinically indolent tumors. The recent discovery of a cutaneous corollary to this tumor suggests that the spectrum of its presentation has not entirely been delineated. In the context of expanding molecular testing, pathologists are tasked to sift through constantly evolving molecular data to incorporate diagnostically relevant tests into their practice. In salivary gland pathology, the example of microsecretory adenocarcinoma demonstrates that primary histologic assessment, with sensible use of immunohistochemistry, can lead to accurate diagnosis. Molecular testing is beneficial in cases with significant diagnostic challenges.