Leiomyosarcoma (LMS) of the thyroid is an extremely rare malignancy, and to have a concurrent papillary thyroid cancer adjacent to it makes it even more extraordinary. We found 39 [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39] reported cases in the literature, with our current case being the 40th, and have analyzed common findings and outcomes within each paper (Table 1). The mean tumor size from available data was 5.88 cm., with the largest tumor measuring 13.5 cm [6]. It is more common in females, with 64.1% out of 39 cases that stated gender were women. Two pediatric cases were reported by Ramakrishnan et al. and Tulbah et al., with the latter demonstrating a rare congenital immunodeficiency with Epstein-Barr virus-induced LMS in multiple organs including the liver, thyroid, and right lung [7, 8]. Only one previous case reported coexisting benign uterine fibroids like in our patient [9]. Four cases illustrated previous history of malignancies [6, 10,11,12]. Piana et al. [12] reported a case who had a previous uterine myxoid LMS and presented 4 years later with thyroid LMS. They argued that the patient’s history strongly indicates a metastasis, however, it was a solitary lesion that had different characteristics from the uterine tumor. They also proposed that there is a chance the patient had two different kinds of LMS originating within two different organs, purely by coincidence.

Most LMS cases present with a neck mass (85% of the cases), followed by compressive symptoms (45% of the cases). Other symptoms include weight loss [5, 13,14,15,16], arm pain [10, 17], neck pain [17], and cervical lymphadenopathy [19]. Akata et al. reported a female case who presented with painless swellings in her body, and she was diagnosed with multicentric synchronous leiomyosarcomatosis due to having multiple nodules in seemingly unrelated organs involving thyroid and salivary glands, pancreas, ligamentum teres, and bones [20]. Regarding the outcome, 55% of the cases were dead with the disease, with the longest duration of survival being 51 months after the diagnosis [21]. Only 15% of the cases had a recurrence of LMS. Furthermore, 25% of the cases reported non-lymph node metastasis most commonly involving the lungs, while 10% of the cases had lymph node metastasis. Ramakrishnan et al. reported an interesting pediatric case who presented with a neck mass, and elevated serum calcitonin, raising a suspicion of medullary thyroid carcinoma [7]. However, histopathology showed an absence of amyloid stroma, and LMS was diagnosed based on immunohistochemistry. Most of the patients (75%) underwent surgery, and 12.5% of the cases received radiotherapy.

The differential diagnosis of thyroid LMS ranges from benign conditions like cysts and adenomas to extremely malignant conditions like anaplastic carcinoma and metastatic lesions. LMS remains an extraordinarily rare tumor of the thyroid, with our case presenting a concurrent PTC. Concurrent PTC tumors with other thyroid pathologies are generally considered coincidental. Thus, Concurrent PTC tumors are regarded as clinically insignificant by expert consensus; however, concrete literature analyses have not yet demonstrated a clear answer. This report demonstrates the importance of being vigilant of the potential diagnosis, especially with immunohistochemical staining. Physicians should look for possible sources of metastasis before labeling a tumor as primary, as the management varies quite heavily.