Introduction

In 1924, Masson and Berger published the first description of mucoepidermoid carcinomas (MEC). With a peak incidence in the fifth decade of life, they are now well acknowledged as a common salivary gland neoplasm, making up around 35% of all malignancies of the major and minor salivary glands in children and young adults. Compared to men, women are more frequently affected.[1] The parotid gland, palate, submandibular gland, and intraoral minor salivary glands are the most often affected sites of MEC.[2] The neural crest gives rise to the highly differentiated melanocytes, which are melanin-producing cells found in the epidermis, hair follicles, uvea, inner ear, vaginal epithelium, meninges, bones, and heart. Melanocytes have also been reported to be present in the normal major and minor salivary glands. [3] These melanocytes are found in the labia minor salivary gland and the parotid glands' interlobular ducts. In the literature, pigmented salivary gland neoplasm is reported only in ten cases. Minor salivary glands were the most often affected site of this pigmented tumor. Here, we present a case of pigmented MEC of the parotid, which was first identified by fine needle aspiration (FNAC) cytology as metastatic malignant melanoma in an operated case of conjunctival melanoma. Immunohistochemistry subsequently revealed that the condition was pigmented MEC.

Case Report

A 72-year-old woman visited the outpatient otolaryngology clinic complaining of preauricular pain and swelling. Upon local examination, a vague 1.5x1.5 cm lump was found to be firm, tender, and slightly movable. (Figure. 1a) Taking into consideration the initial diagnostic tool for any head and neck swelling, FNAC of the mass was advised and carried out by the pathologist. Black aspiration was obtained, which was spread on the slides. Rapid on-site evaluation was done to assess the cellularity. At the same time, a designated pass was taken for the cell block (CB) preparation by the formalin-fixed method. The smears were stained with Giemsa stain (air-dried), hematoxylin and eosin stain, and Papanicolaou stain (wet smears). On microscopy, smears were richly cellular, and tumor cells were arranged in sheets, clusters, and single-cell populations showing marked pleomorphism. The cells were polygonal, having round to oval vesicular nuclei and a moderate amount of cytoplasm. Some of the cells were showing cytoplasmic vacuolation. In addition, the abundant extracellular and intracytoplasmic brown-black color pigment was seen. The background showed numerous mature lymphocytes. (Figure 1b) The CB also showed a similar picture. (Figure 1c) The lack of noticeable inclusion-like eosinophilic nucleoli was the factor that challenged the melanoma diagnosis. After that, the patient underwent further evaluation to determine the primary site of melanoma, and it was discovered that she had undergone conjunctival melanoma surgery 10 years ago. Therefore, the cytology and CB were examined for a possible diagnosis of metastatic malignant melanoma(MM), and immunohistochemistry (IHC) and special stains were carried out. Mucicarmine-stained luminal mucin and pigments were removed with melanin bleach. The diagnosis of MEC, the pigmented type, was confirmed on immunoreactivity for CK, CK7, and MUC-1, and immunonegative status for Melan-A, SOX-10, and CD117. Weak focal positivity for CK5/6, P63, and Ki67 was 60-65%. (Figure. 2)

Figure 1: a: Elderly female with preauricular swelling. b: FNA smears showing tumor cells with entrapped brown-black pigment. (Giemsa stain, 200x), c: Cell block showing tumor cells, some of them showing intracytoplasmic vacuolation. (Hematoxylin and Eosin stain, 200x), d: Gross image showing well-circumscribed black colour lesion in the parotid, e: The section examined shows sheets of tumor cells separated by fibrous septae. (Hematoxylin and Eosin stain, 200x), f: The higher magnification showing tumor cells with intracytoplasmic and extracytoplasmic melanin pigment. (Hematoxylin and Eosin stain, 400x)

Figure 2: Immunohistochemistry

A complete parotidectomy was subsequently sent for histology. The solid dark brown-black tumor measured 1x1x0.7 cm and was well-circumscribed. (Fig. 1d) Sections revealed a well-circumscribed tumor that was arranged in diffuse sheets and divided by thick and thin fibrous septae. (Figure 1e) The tumour cells had the same architecture with the presence of pigments as previously mentioned. (Figure 1f). Metastatic deposits were seen in a single lymph node. There was no evidence of perineural invasion. On cytology, it was difficult to identify pigmented, poorly differentiated MEC in a known case of conjunctival melanoma. Immunohistochemistry and the CB played a crucial role in the diagnosis. This case report is notable because the pigmented MEC is a rare neoplasm in its own right. Additionally, there was a dual pigment-rich malignancy present in this instance, neither of which had a familial history. Both tumors were considered high-grade, and once again, the preparation of CB highlights its importance in the diagnosis and management.

Discussion

Primary malignant salivary gland tumors occur in one out of every 100,000 individuals. Of all the salivary glands, the parotid is the most frequently affected by neoplasms, with about 25% of them being malignant. 25% of cases are of metastatic parotid tumors. Squamous cell carcinoma is the most common type of cancer that spreads to the intraparotid lymph nodes, followed by melanoma and, less frequently, oral cancers. In 7.6-73.3% of cases, parotid cancer metastasizes to intraparotid lymph nodes. Head and neck cutaneous MM are the main cause of metastatic parotid gland melanoma, which often spreads to other body parts. It is believed that more than 75% of parotid metastases spread into the intraparotid lymph nodes of a patient because the parotids function as a filtering centre for lymphatic drainage in the head and neck region. A Google Scholar search and Pubmed search were done using the terms pigmented salivary gland carcinoma/neoplasm and pigmented mucoepidermoid carcinoma. Only ten instances of melanocytes in the parenchyma of major and small salivary gland malignant tumors have been reported to date (Table 1).

The pigment in the gland becomes activated, begins to proliferate, and produces melanin pigment when the salivary gland epithelium goes through a tumorigenic transformation and develops tumors. We do not yet know the precise mechanism by which granules enter the malignant cells. [4] The fact that the melanin granules are found outside the cell membrane gives support to the theory that these malignant cells phagocytose them in a manner akin to that of melanocytes. [5] In this case, the MEC was of the high-grade variety. As seen in CB and resected parotid specimens, cytology showed occasional cells with vacuolated cytoplasm that would have been misinterpreted for cystic macrophages. IHC has not been as effective in diagnosing tumors of the salivary glands. Cytology is highly sensitive and selective for neoplasms of the salivary glands. IHC was essential in this instance, though, as it dramatically altered the diagnosis from melanoma to pigmented MEC.

Conclusion

Although there have been reports of pigmented salivary gland neoplasms, this is the first instance of two cancers being seen simultaneously, which makes diagnosis challenging because both tumor and stromal cells contain intracytoplasmic melanin pigment. Pigmented, poorly differentiated MEC of Parotid gland poses morphological problems, especially in the post-operative context of conjunctival malignant melanoma. Furthermore, this rare pigmented form of MEC may confuse the surgical pathologist. In this instance, the cell block and immunohistochemistry were essential for early diagnosis and treatment planning.

References

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