Study identifies clues to distinguish benign tumor from salivary gland cancer

Analysis of atypical cases suggests that cellular markers may help distinguish Warthin tumor from mucoepidermoid carcinoma

Arthur Almeida

Located near the ear, the parotid gland is one of the major salivary glands and can be affected by both benign and malignant tumors that, in atypical cases, are difficult to distinguish under the microscope | Image: Unsplash

It is not always easy to distinguish a benign tumor from a malignant one based solely on how the cells appear under the microscope. In some cases, tumors with distinct biological behavior can share similar morphological features.

This type of diagnostic challenge can occur in salivary gland tumors, including those affecting the parotid gland, located near the ear.

A study published in April in the journal einstein by researchers at the University of Campinas (UNICAMP), with the participation of a researcher from the University of Utah in the United States, sought to address part of this problem by identifying features that may help distinguish two types of tumors that are often confused: the benign Warthin tumor and mucoepidermoid carcinoma, which is malignant.

Methodology

To reach their conclusions, the researchers analyzed 11 low-grade salivary gland tumors with unusual morphological features resembling those of Warthin tumor.

These tumors displayed characteristics that made it difficult to distinguish between Warthin tumor with metaplastic changes and lymphoid stroma-rich mucoepidermoid carcinoma.

The cases were divided into two groups, designated by the authors as A and B. The main difference between them was the way the cells were organized: in Group A (six cases), a bilayered structure typical of benign Warthin tumor was present in less than half of the epithelial tissue; in Group B (five cases), this organization was absent.

For comparison, the team also analyzed five cases of Warthin tumor and 10 cases of classic mucoepidermoid carcinoma.

In addition to examining the tumors under the microscope, the researchers used a technique called immunohistochemistry. This method works like a “labeling test,” using substances that bind to specific proteins inside cells to reveal patterns that cannot be identified based on cell shape alone.

Study Findings

The results showed that, despite their morphological similarities, tumors in the two groups differed significantly in tissue organization and in the patterns revealed by immunohistochemistry.

Upon closer analysis, the researchers found that the differences were not limited to the tumors’ overall appearance but also involved the cell organization and the distribution of specific markers within the tissue.

Among the cases most closely resembling Warthin tumor, two immunohistochemical markers—the CK7 protein and mitochondrial antigens—showed predominant staining in luminal cells. In Group B, considered more closely related to mucoepidermoid carcinoma, staining tended to be more diffuse throughout the epithelial layers. This difference may help pathologists distinguish between the two types of tumors.

Another important difference was the degree of fibrosis, a type of internal scar tissue surrounding the tumor, which was more common in Group B. This finding suggests that this type of tumor may trigger a stronger tissue response.

The researchers also evaluated the Ki-67 index, which measures how actively cells are proliferating.

Unexpectedly, this index was higher in Group A—the group more closely resembling the benign tumor—reaching 30% in one case, whereas no case in Group B exceeded 5%.

This reinforces the idea that no single marker is sufficient on its own to determine whether a tumor is benign or malignant.

Other markers, including p63, CK14, and CK5/6, also provided useful information, although with varying degrees of overlap between the two groups. For example, p63 showed similar staining patterns in both groups and in the reference cases of mucoepidermoid carcinoma. CK14, meanwhile, helped identify basal cells arranged in a linear pattern, a feature more commonly associated with Group A tumors.

For this reason, the authors recommend interpreting these markers together with CK7 and mitochondrial antigens.

In contrast, these antigens stood out for revealing distinct patterns between the two groups and may become useful tools to support diagnosis. However, the authors emphasize that the findings need to be validated in larger samples.

Impact on patient treatment

One of the study’s main conclusions is that traditional analysis based solely on the cells’ appearance can lead to diagnostic errors because some benign tumors may undergo changes that make them appear malignant, and vice versa.

The authors therefore advocate combining different diagnostic approaches.

Immunohistochemistry helps reveal “invisible” patterns by showing how specific proteins are distributed within cells. Although genetic testing was not performed in all cases included in this study, the authors identify it as an important complementary tool because it can detect DNA alterations in tumors, providing an additional level of diagnostic precision.

One such test looks for alterations in a gene called MAML2, frequently associated with mucoepidermoid carcinoma. Detecting these alterations can provide important molecular evidence supporting this diagnosis when the tumor’s appearance under the microscope remains inconclusive.

The authors point out that MAML2 rearrangement analysis was not performed in all cases as one of the study’s limitations.

Correctly distinguishing Warthin tumor from mucoepidermoid carcinoma is essential because classifying a tumor as benign or malignant directly influences treatment decisions.

The researchers describe the proposed diagnostic criteria as preliminary and argue that studies involving larger sample sizes and more comprehensive molecular testing are needed to confirm their findings.

Reference

Bonfitto JF, Scarini JF, Ferreira IV, de Lima-Souza RA, Egal ES, Altemani A, et al. Preliminary diagnostic criteria for distinguishing metaplastic Warthin tumors from mucoepidermoid carcinomas rich in lymphoid stroma. einstein (São Paulo). 2026; 24: eAO1591. https://dx.doi.org/10.31744/einstein_journal/2026AO1591

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