Outcomes and Characteristics of Mesenchymal Tumors Involving the Parotid Gland

Introduction

Salivary gland tumors are relatively uncommon and widely heterogenous with over 30 pathologically different benign and malignant neoplasms as defined by the Fifth Edition of the World Health Organization Classification of Head and Neck Tumors. ¹ Most salivary gland tumors occur in the parotid gland with proportions ranging from 69% to 80%, and about 50% of malignant salivary tumors are found in the parotid. ²

Both benign and malignant parotid tumors are most often primary epithelial neoplasms but can also occur as metastatic lesions to intra-parotid lymph nodes, or via direct extension from adjacent tissues such as cutaneous tumors, nerve-sheath tumors, or lesions of the mandible or muscles of mastication. Mesenchymal tumors involving the parotid gland are very rare, and given the rarity, can be difficult to formulate treatment plans. These mesenchymal neoplasms may form from the connective tissues of the salivary gland, invade the gland from adjacent sites, or arise from a metastasis. ³ Malignant forms of these mesenchymal tumors have been documented in children, but little has been reported on adults. ⁴ The aim of this study is to identify clinical and pathological factors related to these mesenchymal tumors involving the parotid gland. We hypothesized that identifying clinical and pathological factors related to mesenchymal tumors involving the parotid gland would aid in forming a more effective and appropriate diagnosis and treatment plan.

Methodology

With Institutional Review Board approval (IRB#22-000296), we conducted a retrospective study using a single institution, tertiary referral center, parotid tumor database drawn from all clinical diagnoses, operative reports, and pathology diagnoses from 2001 to 2022. Tumors that were not considered as mesenchymal in origin were excluded from our cohort as were mesenchymal tumors that were considered benign or originated outside the parotid gland and involved parotid tissue only by extension. Data abstracted from our medical records included diagnosis, demographics, pathology, treatment, and follow up information. Tumors were staged according to the AJCC Cancer Staging Manual, Eighth Edition.

Results

Of the 3705 patients who underwent a parotidectomy during this time period, 44 (1.2%) had tumors of mesenchymal origin in or near the parotid. Of these, 8 (18%) were considered malignant and originated from the parotid gland. We excluded the 36 remaining tumors from the study that were either benign or did not originate from the parotid gland.

Patient characteristics are listed in Table 1. There were 3 were males and 5 females, with an average age of 61 years (range = 15-89 years). Our results identified 6 different types of malignant mesenchymal tumors, including 3 pleomorphic sarcomas, and 1 liposarcoma, spindle cell rhabdomyosarcoma, unusual low grade epithelioid mesenchymal neoplasm, inflammatory rhabdomomyoblastic tumor, and undifferentiated spindle cell sarcoma. Recurrences and cause of death are described in Table 2.

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Table 1.

Characteristics of 8 Patients With a Parotid Mesenchymal Tumor and the Associated Tumor Description.

Patient	Age (y)	Sex	Tumor	Site of origin	Smoking history	Tumor size (cm)	Stage
1	89	F	Liposarcoma	Parotid	unk	6.7 × 4.2 × .4.2	T3N0
2	27	F	Spindle cell rhabdomyosarcoma	Parotid	Y	5.1 × 4.4 × 3.4	T2N0
3	77	M	Pleomorphic sarcoma	Parotid	Y	2.2 × 2.1 × 2.0	T2N1
4	81	F	Pleomorphic spindle cell sarcoma	Parotid	Y	1.4 × 0.70	T1N0
5	80	M	Undifferentiated pleomorphic sarcoma	Parotid	N	2.9 × 2.8 × 1.0	T2N0
6	71	F	Undifferentiated spindle cell sarcoma	Parotid	Y	5.6	T3N0
7	15	F	Unusual low grade epithelioid mesenchymal neoplasm	Parotid	N	2.0 × 1.9 × 1.3	T2N0
8	44	M	Inflammatory rhabdomyoblastic tumor	Parotid	N	5.9 × 4.1 × 3.7	T3N0

Abbreviations: F, female; N, no; M, male; Y, yes; unk, unknown.

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Table 2.

Tumor History and Recurrence Outcomes With Associated Disease State and Cause of Death of 8 Patients Diagnosed with a Mesenchymal Parotid Tumor.

Patient	Pathology	Recurrent from prior tumor	Metastasis	Recurrence	Time to recurrence (mo)	Disease state	Time to death (mo)	Cause of death
1	liposarcoma	N	N	LTFU	LTFU	LTFU	LTFU	LTFU
2	Spindle cell rhabdomyosarcoma	N	N	Regional, Distant	2	AWD, 43	unk	unk
3	Pleomorphic sarcoma	N	N	N	na	AWOD	na	na
4	Undifferentiated spindle cell sarcoma	N	N	N		Death	2	other
5	Undifferentiated pleomorphic sarcoma	Y	N	Local, Distant	10	Death	19	Sarcoma
6	Undifferentiated spindle cell sarcoma	N	N	Regional, Distant	14	AWD	na	na
7	Unusual low grade epithelioid mesenchymal tumor	N	N	N	na	AWOD	na	na
8	Inflammatory rhabdomyoblastic tumor	N	N	LTFU	LTFU	LTFU	LTFU	LTFU

Abbreviations: AWD, alive with disease, months of documentation post procedure; AWOD, Alive Without Disease; LTFU, lost to followup; N, no; na, not applicable; Y, yes.

A preauricular/cheek mass was the most common presentation, found in 7 patients. Facial pain was present in 3 patients, while 4 experienced symptoms of otalgia on the ipsilateral side. Aural numbness was present in 1 patient, while 3 experienced aural fullness or hearing changes.

The initial diagnosis of a malignant mesenchymal parotid tumor was based on imaging from either a CT or an MRI along with either an excisional/incisional biopsy or fine needle aspirate (FNA). FNA was performed in 3 patients while 2 patients received an excisional biopsy. All excisional biopsies were done outside of our institution and were reviewed by the Head & Neck Pathology group at the authors’ institution. FNA was nondiagnostic in all 3 cases and identified a malignancy of mesenchymal origin in only 2 of the 3 cases. The 1 case which was nondiagnostic with no identification of tissue origin consisted of an unusual low grade epithelioid mesenchymal neoplasm. Diagnosis was confirmed with histopathological examination upon resection of the tumor.

The type of parotidectomy performed was based upon the region of the tumor and its position along the parotid gland, as well as the presence or concern for lymphadenopathy. Superficial parotidectomy and total parotidectomy were performed in 4 patients each. The facial nerve was preserved in all 8 patients. The average size of the resected tumors at its greatest dimension was 3.98 cm (range = 0.70-6.7 cm).

Four patients received post-operative radiation, including 2 patients with pleomorphic sarcoma, 1 patient with spindle cell rhabdomyosarcoma, and 1 patient with undifferentiated spindle cell sarcoma (Table 3). The rationale for radiation among the 4 patients consisted of either having positive surgical margins, close surgical margins and perineural invasion, nodal metastasis, or an external hospital’s recommendation. In 1 case, a patient diagnosed with pleomorphic spindle cell sarcoma received neoadjuvant radiation to reduce the size and operability of the tumor before surgery. Postoperatively, 6 patients reached a House-Brackman (HB) scale of I at the time of last follow up, while 2 patients reached HB II. Median time to last follow up was 2.4 years (range = 0.01-6.1 years). Treatment courses and associated radiation doses are summarized in Table 3.

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Table 3.

Radiation Courses of 8 Patients With a Diagnosed Mesenchymal Parotid Tumor.

Patient	Pathology	Neoadjuvant treatment	Adjuvant treatment	Radiation dose (cGY)
1	Liposarcoma	N	N	na
2	Spindle cell rhabdomyosarcoma	N	Chemoradiation	unk
3	Pleomorphic sarcoma	N	Radiation	6000-6400
4	Undifferentiated spindle cell sarcoma	Radiation (5000 cGy)	N	na
5	Undifferentiated pleomorphic sarcoma	N	Radiation	5000
6	Undifferentiated spindle cell sarcoma	N	Radiation	6600
7	Unusual low grade epithelioid mesenchymal tumor	N	N	na
8	Inflammatory rhabdomyoblastic tumor	N	N	na

Abbreviations: N, no; na, not applicable due to the patient not receiving radiation; unk, unknown; Y, yes.

There were 3 recurrences that arose on average 8.6 months after the initial tumor resection (Table 2). There were 2 instances of distant recurrence in the lungs, and 1 report in the pancreas and breast. Among the 3 patients, there were 2 additional cases of regional recurrence that occurred in the paratracheal nodes. Death was confirmed in 2 patients. In 1 case, the patient died from their disease and the other due to causes unrelated to their disease.

Discussion

Pleomorphic sarcoma was the most common primary parotid mesenchymal tumor, accounting for 38% of malignant mesenchymal tumors in our series. Preauricular cheek mass and otalgia were the most common presenting signs. Local control was achieved in most patients after surgery, with only 1 patient presenting with local recurrence following surgical resection and radiation. However, 2 patients developed regional recurrence and 3 developed distant recurrence in an average time of 8 months. Postoperatively, 2 patients demonstrated temporary facial paresis which recovered to HB II, with no observed instances of permanent facial paralysis. Surgical resection with or without adjuvant radiation and close follow up within the first 2 years of diagnosis may provide meaningful local control for patients with malignant mesenchymal parotid tumors.

There is scant literature regarding malignant mesenchymal tumors of the parotid glands. Our database of patients undergoing surgery for parotid tumors, only 8 of 3705 (<1%) tumors were malignant mesenchymal tumors. Wang et al ² reported on 2508 salivary gland tumors, none of these were mesenchymal in origin. Velez Torres et al ³ reported on 68 cases of benign and malignant mesenchymal tumors of the parotid, 5 of these were malignant, 3 being Adamantinoma-like Ewing sarcomas.

In our cohort, 3 patients received FNA biopsies while 2 received an excisional biopsy. When differentiating between malignant and benign parotid neoplasms, a review by Schmidt et al, ⁵ FNA had a sensitivity of 0.83 in 9 US studies and 0.79 in 55 non-US studies. However, variability across study sites and diagnostic biases limit conclusions about its true accuracy. FNA can be limited by sampling errors and low cellularity. ⁶ In our series, FNA correctly identified mesenchymal tumor origin in 66% (2/3) of malignant parotid mesenchymal neoplasms. Sensitivity may vary by tumor type, as FNA has diagnosed sarcomas in as few as 21% of cases, whereas core needle biopsy achieves higher accuracy due to greater tissue yield and improved immunohistochemical analysis.^7,8 The low FNA accuracy in our series underscores the diagnostic challenges of parotid mesenchymal tumors.

All patients in this series underwent parotidectomy. Five patients received at least 1 course of radiation therapy and 1 of these patients also received chemotherapy concurrently. Sarcomas involving the parotid gland are rarely amenable to aggressive, wide-margin surgery, due to the presence of critical neurovascular structures. As demonstrated by the 4 patients in this study, close or positive margins, high grade histology, recurrence, and regional disease often dictate adjuvant therapy. Zagars et al ⁹ reported on conservative surgery and adjuvant radiation for soft tissue sarcoma and reported survival rates of 73% at 5 years and 68% at 10 years.

In our series, pleomorphic sarcoma comprised 3 of the 8 tumors and were more common in males. All 3 patients underwent tumor resection and received either neoadjuvant or adjuvant radiation therapy, and 1 patient developed a recurrence. Pleomorphic sarcomas are formed from histiocyte proliferation in a storiform growth pattern and are typically high grade, affecting mostly males between 50 and 70 years old.^10,11 Boccalatte et al, ¹⁰ reported poor prognostic factors with age >60 years, tumor size >5 cm, and high-grade histology. The study also found that margin status and histologic grade factored into recurrence while histologic grade and age factored into survival. Resection remains the standard treatment, with adjuvant radiotherapy improving local control, despite 1 recurrence in our series. ¹¹

This study has several limitations. Small sample size, rarity of the tumors, heterogeneity of pathology, and lack of follow-up in 25% of patients limits any conclusions.

Conclusion

Malignant mesenchymal parotid tumors are uncommon salivary neoplasms that vary in their histopathology and clinical course. In our series, pleomorphic sarcoma was the most common histology, and distant metastasis was the predominant recurrence. Given their aggressive nature, surgical resection with radiotherapy for high-risk cases, along with close follow-up, may offer adequate local disease control. By defining clinical signs and symptoms of malignant parotid mesenchymal tumors, diagnosis and treatment can be more specifically tailored to the patient in hopes of obtaining a more favorable outcome.