Surgical Treatment of Malignant Transformation Tumors of the Parotid Salivary Gland of the Large Size from 30 Years Ago

New salivary gland formations are rare and account for approximately 3-6% of all head and neck tumors. The incidence of salivary gland cancer in the United States is approximately 2.5-3 cases per 100,000 populations per year [1]. 

In 2021, for the first time, 125 cases of malignant tumors of the salivary glands were recorded in the Republic of Uzbekistan, with an incidence of 0.4 per 100,000 populations [2]. 

Pleomorphic adenoma is the most common benign neoplasm of the salivary glands [3]. However, pleomorphic adenoma can undergo malignant transformation into ex pleomorphic adenoma [4-6]. The risk of malignant transformation increases with longstanding tumors. 

Untreated large parotid salivary gland tumors are rare, and this clinical case highlights a patient with a 30 year-old pleomorphic parotid salivary gland adenoma with malignant transformation who successfully underwent surgery.

This is a 73-year-old patient who contacted the Ferghana regional branch of RSSPMCO&R MoH RUz, Ferghana, Uzbekistan, in May 2022 with complaints of a large hanging mass in the left parotid region and the presence of a bloody wound on the skin of the inferior side of the mass (Figure 1).

 Figure 1: Patient 73 years before treatment. 

From history, the tumor appeared 30 years ago and initially grew slowly. Recently, however, the tumor began to grow quickly. Since it was painless, the patient did not visit a physician for evaluation. Between April-May 2022, an open wound appeared on the inferior side of the tumor and had associated intermittent bleeding, prompting the patient to seek medical care. Preoperative clearance was obtained, and the patient was scheduled for surgery a month in advance, keeping in consideration factors such as older age, continuous bleeding from the tumor, and history of poorly controlled hypertension. After the bleeding wound healed and hypertension was successfully treated, the patient underwent surgical resection. 

Preoperative Multiple-Slice Computed Tomography (MSCT) of head, dated 05.11.2022 (Figure 2), showed parotid and cervical region on the left with multiple formations of a rounded irregular mass, measuring from 18×24 mm to 93×108 mm. Density + 34+64 µN. The contours are uneven. Conclusion: CT signs of multiple parotid salivary gland lesions on the left.

 Figure 2: CT in 3 projections. A large tumor emanating from the left parotid salivary gland. 

Fine-needle aspiration cytology (FNAC) revealed a salivary gland tumor that is uncertainly benign (Milan classification 4b). Suspicion for salivary gland pleomorphic adenoma. 

Ultrasound examination of the left parotid region on 05.11.2022 revealed a mixed echogenic multiple formations of sizes ranging from 20×25 mm to 95×120 mm. Nodes of the ear area with dimensions of 35 x 26 mm are also defined. Peripheral lymph nodes are not visualized. 

Status localis: on the left parotid region there is a large hanging tumor and on the inferior side of the tumor a healed wound is identified (Figure 1). The overall tumor size is 22×12×12cm and consists of several parts. The largest tumor formation resembles the shape of a hanging ball. Despite the large size of the tumor, there was no weakness (paresis) of facial muscles innervated by the facial nerve. Regional lymph nodes were not palpable. 

After FNAC, the patient was diagnosed with pleomorphic adenoma of the left parotid salivary gland and underwent subtotal resection of the left parotid salivary gland in June 2022. Tumor was resected carefully to avoid integrity of the branches of the facial nerve. In the postoperative period, a satisfactory aesthetic and functional result was achieved without signs of facial paralysis, and the patient was discharged home. Figure 3 shows the gradual removal of the parotid salivary gland.

 Figure 3: Phased removal of the left parotid salivary gland. 

When examining the macro-preparation, the tumor has an oval shape measuring 22×12×12 cm. The middle section revealed tumor decay with hemorrhagic fluid (Figure 4).

Figure 4: Macro-preparation: a. Resected tumor, b. Tumor in the section view, c. Tumor in the sectional view after removal of hemorrhagic contents.

Histopathological examination reported two components of the tumor - epithelial and mesenchymal (myxoid); ducts from epithelial, located in several layers dissolve in the myxoid stroma. Evidence of foci of extensive inflammation and necrosis, angular fusiform nuclei, some hyperchromicity with an increase in mitotic figures and some cellular atypia. 

Postoperative Histology 5798-5809/2022: Pleomorphic adenoma with malignization (Figure 5).

Figure 5: A. Histopathology. Ducts from epithelial cells, located in several layers, dissolve in the myxoid stroma. Uv.200. H&E. B. sites with extensive inflammation and necrosis, angular fusiform nuclei, enlargement of mitotic figures, and some cellular atypia. Uv.400. H&E.

The postoperative course was uneventful (Figure 6).

 Figure 6: Same patient 20 days after surgery.

Patients with a long-existing pleomorphic adenoma that begins to grow rapidly or become painful are rare, suggesting the development of cancer growing in the primary tumor via malignant transformation of the pleomorphic adenoma. Histologically, it will be a clearly malignant tumor, usually a low-differentiated adenocarcinoma, mucoepidermoid cancer, or another type of malignant tumor [1]. In this case, the histology results suggested that the pleomorphic adenoma had a malignant transformation over time. 

Salivary gland tumors can be complex and vary in terms of their morphological spectrum. Although this type of tumor is most frequently encountered, it is still rare (European Standardized rate: 4.5/100,000 as opposed to 62/100,000 seen in breast cancer) [7]. The diagnosis can be challenging owing to its morphological similarity with features of other 22 salivary gland carcinomas [8-10]. 

However, a notorious feature among these cancers is the malignant transformation of the most common salivary gland tumor, pleomorphic adenoma, to carcinoma ex-pleomorphic adenoma, which is the fifth most common salivary gland tumor [10-12]. This diagnosis is made based on finding pleomorphic adenoma components in the malignant tumors and are therefore classified as carcinoma ex-pleomorphic adenoma. The morphological as well as molecular transitions are seen from the benign pleomorphic adenoma component to the malignant carcinoma component [10,13-17]. 

This type of neoplasm can lead to dilemmas in both pathological diagnosis and surgical/adjuvant radiation treatment of primary and recurrent pleomorphic adenoma. This risk of malignant transformation is, however, rare, as only 3% of salivary pleomorphic adenomas recur at 12.5-year follow-up, of which approximately 6% seem to show malignant transformation [11]. Furthermore, Valstar MH, et al noted that a malignant transformation occurred in 1.1% of primary and 0.15% of secondary salivary gland pleomorphic adenomas after 5 years of dynamic follow-up (3.2% of all relapses) [7]. Similar results were seen from a study in Denmark, showing 1.7% malignant transformation with a mean 6.2% risk, but the data was acquired from a single-center study, which can reflect a referral bias [10,18,19].

Malignant transformation of pleomorphic adenoma of parotid gland can occur over a long period of time. Left untreated, pleomorphic adenomas can continue growing in size, increasing the risk of malignant transformation. The frequency of malignant transformation, however, varies, based on different study results. This case report highlights that within 30 years of untreated tumor growth, malignant transformation occurred as was evidenced by morphological features of the tumor as well as histological examination. The main method of treatment is surgical removal of the tumor.

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