Rare Salivary Tumors Hide Two Cancerous Components, Case Reports Show

Two case reports of carcinoma ex pleomorphic adenoma, a rare malignant transformation of a salivary gland tumor, found that each excised mass contained two distinct cancerous components. The tumors arose in the palate of a 74-year-old woman and the parotid gland of a 53-year-old woman. In both cases, clinical examination and non-contrast computed tomography could not determine the tumor’s nature, while postoperative histopathology revealed a benign pleomorphic adenoma background alongside two morphologically distinct carcinomas. The first tumor combined mucoepidermoid carcinoma and solid-type adenoid cystic carcinoma; the second combined mucoepidermoid carcinoma and salivary duct carcinoma. Their unusual composition illustrates why extensive sampling and multiple diagnostic methods were needed to classify the lesions.

The first patient had noticed a palatal mass approximately four years before presentation. It had enlarged painlessly during the preceding six months and had never been treated. Clinical examination found a firm, poorly defined, non-tender mass about 2.5 by 2.5 by 2 cm beneath intact, smooth mucosa with mild redness but no visible ulceration. Non-contrast CT demonstrated an irregular palatal mass. During surgery on October 8, 2020, the lesion was excised and measured 2.0 by 2.0 by 1.5 cm. The operative specimen was submitted for pathological examination, and no major surgical complication was documented in the available records.

Microscopic analysis showed a tumor with unusually varied architecture and multiple cell populations. Glandular cells, mucus within gland-like spaces, and myxoid tissue were mixed with sheets of mucoid and epidermoid cells and solid epithelial nests. Some larger nests had central necrosis and visible mitotic figures. These findings supported the presence of mucoepidermoid carcinoma, while a solid growth pattern and myoepithelial features supported an adenoid cystic carcinoma component. The final diagnosis was palatal carcinoma ex pleomorphic adenoma containing both components. Quantitative mitotic count, reliable margin status, lymphovascular invasion, depth of invasion, overall histological grade and complete pathological stage were not preserved in the archived records.

The second patient was 53 years old and had carried a right parotid-region mass for more than two years before it began enlarging painlessly over six months. The mass measured approximately 5.0 by 5.0 by 3.0 cm on clinical examination and produced visible facial asymmetry with mild weakness at the right corner of the mouth. No enlarged lymph nodes were palpable, and parotid duct secretion was normal. CT showed a well-defined soft-tissue mass in the right parotid gland. A right superficial parotidectomy with tumor excision was performed on March 8, 2019; intraoperatively, the mass measured 4.0 by 4.0 by 3.0 cm and was adherent to facial nerve branches.

Pathology in the parotid specimen revealed myxochondroid stroma, glandular epithelium, myoepithelial cells, mucous and epidermoid cells, mucin pools, cribriform architecture and solid nests with prominent “comedone-like” central necrosis. The authors classified the lesion as carcinoma ex pleomorphic adenoma with mucoepidermoid and salivary duct carcinoma components. Its Ki-67 proliferation index was approximately 15%. As in the palatal case, the records did not reliably establish histological margins, perineural or lymphovascular invasion, depth of invasion, grade or complete pathological stage. Neither patient underwent neck dissection, so pathological nodal status and extranodal extension could not be evaluated.

Both cases illustrate a central limitation of preoperative evaluation. Imaging can describe a salivary gland mass, but it cannot reliably expose every malignant region inside a heterogeneous tumor. The palatal lesion looked irregular on CT, whereas the parotid lesion appeared clearly demarcated, yet neither appearance established its exact pathology. The authors note that fine-needle aspiration and limited biopsy may also miss one component by sampling only part of the lesion. Their differential diagnoses included pleomorphic adenoma and several other benign or malignant salivary gland tumors, but the final classification depended on identifying benign pleomorphic adenoma tissue alongside two separate malignant morphologies. The diagnoses were therefore retrospective, based on examination of the surgically removed tumors rather than clinical or radiological appearances alone.

Immunohistochemistry and special staining supplied supportive evidence but were interpreted alongside the tissue architecture rather than as stand-alone tests. In the palatal tumor, staining for CK34βE12, CK5/6, p63, GFAP and smooth muscle actin was positive, while CD10 and desmin were negative. In the parotid tumor, S-100, CK7, EMA, p63, calponin, estrogen receptor and p53 were positive; CD117 and progesterone receptor were negative, and mucicarmine highlighted mucin production. The authors regarded mucoepidermoid differentiation as primarily morphologic, supported by the mucinous and epidermoid cells, mucin stains and epithelial markers. They similarly based the adenoid cystic and salivary duct components primarily on characteristic histomorphology, using the available stains as corroboration.

Fluorescence in situ hybridization supplied molecular support for the shared pleomorphic adenoma lineage. Break-apart rearrangements of the PLAG1 gene locus were detected in 86% of tumor cells in the palatal case and 85% in the parotid case. The authors interpreted PLAG1 rearrangement as evidence supporting carcinoma ex pleomorphic adenoma rather than as a specific marker for mucoepidermoid carcinoma. This distinction matters because the tumors contained multiple histologies. The combined evidence—clinical history, imaging, broad histologic sampling, immunohistochemistry, special stains and PLAG1 FISH—was used to separate the cases from pure mucoepidermoid carcinoma, adenoid cystic carcinoma, salivary duct carcinoma and other salivary gland malignancies.

Both tumors were grossly excised, and neither patient received postoperative radiotherapy, chemotherapy or another systemic antitumor treatment. The reasons for omitting neck dissection and adjuvant therapy were not documented and were not retrospectively inferred. During available follow-up, no local recurrence or distant metastasis was identified: the palatal patient was followed for three years and the parotid patient for two years. These outcomes describe only the documented observation periods and do not establish a general treatment effect. Detailed imaging, laboratory results and structured patient-reported outcomes were not systematically preserved, while the two cases cannot show whether similar outcomes would follow other patients. The report’s value lies instead in exposing a rare diagnostic pattern and identifying the information lost when pathological records are incomplete.

Recognizing dual malignant components has practical implications even though this report does not test a treatment strategy. Adenoid cystic carcinoma has a recognized tendency toward perineural invasion and distant metastasis, whereas salivary duct carcinoma may display aggressive local behavior and a comparatively high rate of regional lymph-node metastasis. Identifying all components, together with margins, depth of invasion, perineural and lymphovascular invasion and nodal status, may therefore inform risk assessment and multidisciplinary planning. The authors emphasize extensive sampling of resection specimens and careful review of morphologically distinct areas so that one component does not obscure another. Their literature review indicates that most carcinoma ex pleomorphic adenomas contain one malignant component, making the paired histologies reported here exceedingly uncommon. The two cases show that a seemingly routine salivary gland mass can conceal several cancers at once, and that accurate diagnosis can require the full diagnostic chain rather than imaging or a single laboratory marker alone.

Subject of Research: Dual malignant components in carcinoma ex pleomorphic adenoma

Article Title: Carcinoma ex pleomorphic adenoma containing two cancerous components: two case reports

Article References: Mou, Q., Li, D., Qin, D., Li, K., Nie, M., Liu, Y., & Liu, X. (2026). Carcinoma ex pleomorphic adenoma containing two cancerous components: two case reports. Frontiers in Oncology, 16, Article 1981963. https://doi.org/10.3389/fonc.2026.1981963

Image Credits: AI Generated

DOI: 10.3389/fonc.2026.1981963

Keywords: carcinoma ex pleomorphic adenoma, salivary gland cancer, pleomorphic adenoma, mucoepidermoid carcinoma, adenoid cystic carcinoma, salivary duct carcinoma, PLAG1 rearrangement, histopathology, case reports, Carcinoma, pleomorphic, adenoma