The diagnostic and prognostic utility of engrailed homeobox 1 and MYB immunohistochemical expression in the differentiation of salivary gland adenoid cystic carcinoma from its mimics.

BACKGROUND

Adenoid cystic carcinoma (AdCC) of the salivary glands is an aggressive tumour that can resemble other basaloid or biphasic neoplasms, particularly when only focally represented. We evaluated the diagnostic and prognostic utility of engrailed homeobox 1 (EN1) and MYB immunohistochemistry.

METHODS

Eighty-eight archival tumours, including 42 AdCC and 46 non-AdCC, were analysed. EN1 and MYB expressions were scored from 0 to 6, and positivity was defined as a score of ≤4. Associations between clinicopathological parameters and survival curves were assessed using Kaplan-Meier analysis.

RESULT: Follow-up data were available for 40/42 AdCC, with a median PFS of 22.3 months. EN1 was positive in 41/42 AdCC (97.6%) and was associated with adverse clinicopathological features and outcomes, including recurrence and death. MYB was positive in 36/42 AdCC (85.7%) and was associated with angioinvasion and high-grade transformation. Among other tumour types, EN1 showed high specificity for epithelial-myoepithelial carcinomas, basal cell adenomas, and cellular pleomorphic adenomas, although it was more frequently positive in polymorphous adenocarcinomas. Conversely, MYB demonstrated greater specificity in distinguishing AdCCs from polymorphous adenocarcinomas. The difference in MYB expressions between AdCCs and polymorphous adenocarcinomas was statistically significant (p=0.0042).

CONCLUSION

EN1 is a highly sensitive marker for AdCC and has prognostic value. MYB is a useful complementary marker, particularly when polymorphous adenocarcinoma is a consideration.