Dear Editor,
On September 2018, a case report titled “Squamous cell carcinoma arising from a sebaceous cyst” was published in the “Journal of Surgery and Trauma” (volume 6, issue 2) (1). It was an interesting article; however, I think when dealing about such rare tumors, it is important to be aware of other diseases, such as proliferating trichilemmal cysts (PTC) that may be confused with squamous cell carcinoma arising from a cyst. Trichilemmal (pilar) cysts are common in the scalp. These cysts originate from the outer root sheath of the hair follicles. Although trichilemmal cysts are benign, they can be transformed to PTC as a result of trauma and inflammation (2). The PTCs appear as intradermal masses with a size range of 1-10 cm. They may affect the overlying skin through fistulization or leave it intact. There are some reports regarding PTCs as fungating tumors with a diameter of 25 cm (3, 4). The PTCs can also have an invasive and malignant behavior, and therefore be called malignant PTCs (MPTCs). The MPTCs are reported to be accompanied with local invasion, metastasis to the lymph nodes, and distant metastases (5). Treatment of benign PTC involves a simple excision; however, the management of MPTCs requires surgical procedures with a safe excision margin of 1 cm (6, 7). Mohs micrographic surgery may increase the chance of the complete removal of the tumor (8). In addition to the excision of the tumor with a wide margin, other therapeutic modalities, such​as lymph node dissection, radiotherapy, and chemotherapy, should be also considered for the treatment of MPTC (3, 8-10). In metastatic cases resistant to the above therapies, ethanol injection into the lesions has been used to control the disease (11).