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18 March 2015 - Case of the Week #346

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Thanks to Dr. Ashima Agarwal, SSM Cardinal Glennon Childrens Hospital, Missouri (USA), for contributing this case. To contribute a Case of the Week, follow the guidelines on our Case of the Week page.


  • Differential Diagnoses in Surgical Pathology: Gastrointestinal System (2015) by Elizabeth A. Montgomery, Whitney M. Green. Systematically solve tough diagnostic challenges in GI pathology with Differential Diagnoses in Surgical Pathology: Gastrointestinal Tract! This clinical reference in the Differential Diagnoses in Surgical Pathology Series uses select images of clinical and pathological findings together with succinct, expert instructions, to guide you through the decision-making process by distinguishing between commonly confused Gastrointestinal lesions.

  • Biopsy Interpretation of the Uterine Cervix and Corpus (Biopsy Interpretation Series, 2015) by Anais Malpica, Elizabeth D. Euscher. Part of the comprehensive Biopsy Interpretation Series, the second edition of Biopsy Interpretation of the Uterine Cervix and Corpus provides an easy-to-follow, practical approach to normal histology, non-neoplastic conditions, and neoplasia of the cervix and uterine body. Focusing on the most common biopsies, this up-to-date bench reference emphasizes morphologic features and immunohistochemistry in the diagnostic material, with close attention paid to differential diagnosis, including benign mimics of tumors.

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Case of the Week #346

Clinical History:
A 4 year old boy presented with a partially cystic mass in the soft tissue of the right cheek, adjacent to the right parotid duct.

Micro images:

What is your diagnosis?

Mucoepidermoid carcinoma, clear cell variant, low grade


Immunostains were obtained:



Mucoepidermoid carcinoma is the most common malignant salivary gland tumor, and also the most common radiation induced neoplasm. Although all tumors are considered malignant, low grade tumors have an excellent prognosis and rarely metastasize, and high grade tumors have a high risk of recurrence, metastases and death. These tumors frequently have a t(11;19)(q21;p13) translocation, causing a CRTC1-MAML2 fusion, which is associated with lower stage tumors and better prognosis (Cancer Genet Cytogenet 1994;74:77, Mod Pathol 2013;26:213).

Mucoepidermoid carcinomas are composed of cords, sheets and clusters of mucous, squamous, intermediate and clear cells. Tumors vary from low to high grade. Low grade tumors typically have mucinous and intermediate cells with bland nuclei forming glandular spaces. High grade tumors have solid and infiltrative growth patterns of atypical epidermoid and intermediate cells with cytoplasmic clearing and small number of mucinous cells, but typically lack marked nuclear atypia, frequent mitotic figures or extensive necrosis (Am J Surg Pathol 2001;25:835, Head Neck Pathol 2013;7:105). High stage and nodal status are poor prognostic factors.

The differential diagnosis includes salivary gland duct carcinoma (typically negative for androgen receptor and positive for p63 and CK5/6 (Head Neck Pathol 2014;8:133). Other clear cell tumors of the Head and Neck include clear cell carcinoma and clear cell variants of acinic cell carcinoma, epithelial-myoepithelial carcinoma, myoepithelial carcinoma, and oncocytoma. The differential diagnosis also includes metastatic renal cell carcinoma and balloon cell melanoma.

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