A symptomatic intercalated duct lesion of the parotid gland: a case report with immunohistochemical and genetic analyses

A Subset of Salivary Intercalated Duct Lesions Harbors Recurrent CTNNB1 and HRAS Mutations: A Molecular Link to Basal Cell Adenoma and Epithelial-Myoepithelial Carcinoma?

BACKGROUND

Intercalated duct lesions (IDLs) are benign salivary gland proliferations that resemble normal intercalated ducts and are subdivided into hyperplastic, adenoma or hybrid types depending on circumscription. While IDLs were historically regarded as non-neoplastic, frequent association with basal cell adenoma (BCA) and epithelial-myoepithelial carcinoma (EMC) has raised the possibility that they are neoplastic precursors.

METHODS

In this study, we performed β-catenin immunohistochemistry and targeted molecular analysis on IDLs to clarify their pathogenesis.

RESULTS

We identified 15 IDLs from the parotid glands of eight men and six women with a median age of 65 years (range 42-85 years). These lesions included nine hyperplastic, three adenoma, and three hybrid types. Nuclear β-catenin localization was present in 7 of 13 lesions tested (54%). Next generation sequencing was successfully completed in 12 IDLs, of which seven (58%) had likely oncogenic mutations. These included three recurrent CTNNB1 mutations in hyperplastic (n = 2) and hybrid (n = 1) lesions and two recurrent HRAS hotspot mutations in adenomas.

CONCLUSION

Despite substantial heterogeneity, these findings confirm that a majority of IDLs are genuinely neoplastic, and some demonstrate molecular overlap with both BCA and EMC, supporting their theorized role as precursors to these tumors. Nevertheless, no oncogenic drivers were present in a significant subset of cases, suggesting that some IDLs may be truly reactive and hyperplastic. As such, IDL appear to represent a diverse morphologic and molecular spectrum that include both neoplastic and hyperplastic lesions. Reconsideration of the boundary between IDL and BCA in the future may be necessary to simplify classification.

Hybrid intercalated duct lesion of the parotid: A case report

BACKGROUND

Intercalated duct lesions (IDLs) are considered relatively benign and rare tumors of salivary glands, that were only described recently. Their histopathological appearance may range from ductal hyperplasia to encapsulated adenoma with hybrid patterns of both variants. It is thought that IDLs may be the precursor for malignant proliferations, therefore their correct diagnosis remains crucial for proper lesion management. It is the first reported IDL case arising from the accessory parotid gland (APG), which stands for less frequent but higher malignancy rate tumor developmental area.

CASE SUMMARY

A 24-years-old male with no accompanying diseases was referred to the hospital with a painless nodule on the right cheek. On physical examination, the stiff, immobile, and painless mass was palpable in the anterior portion of the right parotideomasseteric region, just superior to the parotid duct. Ultrasound examination demonstrated 1.5 cm × 1.0 cm hypoechogenic mass on the anterior part of the right parotid gland. Ultrasound-guided fine needle aspiration cytology, followed by liquid-based fine needle aspiration biopsy were performed. However, the results were uninformative. A contrast-enhanced magnetic resonance imaging (MRI) of the parotid was obtained, demonstrating a 1.5 cm × 1.0 cm × 0.5 cm tumor with high intensity capsule together with low intensity core in the very anterior part of right superficial lobe, situated in the APG. An MRI features were uncharacteristic to common parotid tumors, therefore surgical resection followed up. After histopathological examination, the final diagnosis of hybrid IDL was confirmed.

CONCLUSION

Fine needle aspiration biopsy might not always be diagnostic, and given the malignant potential, the surgical resection of such lesion remains the treatment of choice.