Extensive Bone Destruction, Lymphovascular and Perineural Invasion, and Local Recurrence: Unusual Features in Salivary Gland Microsecretory Adenocarcinoma.

PURPOSE: Microsecretory adenocarcinoma (MSA) is a recently described salivary gland adenocarcinoma with distinctive histological features and novel genetic signature viz. MEF2C::SS18 fusion. Archival diagnoses are most frequently adenocarcinoma, not otherwise specified (NOS) and polymorphous adenocarcinoma (PAC). To date, most documented MSA cases have shown indolent behaviour, supporting their categorization as low-grade adenocarcinomas.

METHODS

Molecularly confirmed cases of MSA with unusual clinical and histological features indicative of aggressiveness are described. Archival cases of adenocarcinoma NOS and PAC were assessed to identify potential MSA cases.

RESULTS

Three MSA cases showed features of aggressiveness: large size, extensive bone destruction and lymphovascular invasion in one case; perineural invasion in two cases; and predominance of solid architecture and local recurrence in one case. One patient died of unrelated causes; the other two are disease-free at 40 and 31 months, respectively. Review of six adenocarcinoma NOS and 14 PAC did not yield any potential cases of MSA. FISH for SS18 rearrangement was negative in all adenocarcinoma NOS.

CONCLUSIONS

Bland cytomorphological features typical of fusion-associated neoplasms do not preclude presence of aggressive histological features and development of recurrence in MSA. These aggressive features may serve as indicators for escalation of treatment, despite the low-grade appearance of MSA.