Discussion
EMC has many histologic variations, thereby rendering an accurate
diagnosis difficult.2 Immunohistochemical staining is
of limited value in differentiating EMC from other salivary gland tumors
with biphasic differentiation; however, HRAS mutation testing may
increase the rate of accurate diagnosis.
HRAS mutations are present in 81.7% of EMCs; however, noHRAS mutations have been identified in EMC-like salivary gland
tumors, such as ACC, pleomorphic adenoma, BCA/BCAC, and myoepithelial
carcinoma.2 Herein, both cases lacked characteristic
features of EMC, but the presence of HRAS mutations led to a
diagnosis. Additionally, we could distinguish EMC from its histologic
mimic more accurately by confirming the absence of β-catenin nuclear
reactivity observed in BCA/BCAC and the lack of MYB mutations,
which indicate ACC. Notably, there is no significant correlation between
the HRAS mutation status and histologic indicators of tumor
aggressiveness.2
EMC is generally low-grade; however, ‘high-grade transformations (HGTs)’
have been reported.1, 3 Dedifferentiation of salivary
gland tumors has been described as HGTs, where a low-grade carcinoma
results in a secondary high-grade carcinoma, which is associated with a
worse prognosis. In case 2, a high degree of necrosis, numerous mitoses,
and a high Ki-67 LI were seen, indicating that it was a high-grade
tumor. It was difficult to conclude that it was an HGT of EMC based on
the histopathological features; however, the HRAS mutation led to
the diagnosis of EMC.
The standard treatment for EMC is complete surgical resection. The
prognosis is relatively good in patients who have undergone wide
surgical resection with clear margins.4
Conclusion
Genetic analysis for HRAS mutations is a crucial adjunct to
pathological diagnosis of EMC and may play a decisive role, especially
in difficult-to-diagnose cases.
Authors’ Contributions
Taisei Yasuda : concept/design, analysis of patient data,
drafting and revision of the manuscript, final approval of the
manuscript
Masami Osaki : analysis of patient data, drafting and revision
of the manuscript, final approval of the manuscript
Masahiko Sugitani : analysis of patient data, drafting and
revision of the manuscript, final approval of the manuscript