Epidermoid cysts (ECs) are usually slow-growing, painless, cutaneous lesions that account for 85–95% of all excised cysts [1]. Although ECs are usually benign, they can rarely transform into malignant lesions. Malignant transformation can occur and it accounts for 1% of the cysts. Squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) were reported.

A 57-year-old Syrian female patient presented with a huge mass on the back. On clinical examination, the patient was in a good general status. She had a solitary large mass in the trunk region, which occupied most of the left region of the back measuring approximately 25.0 × 20.0 cm. On palpation, the mass was tender; found to be soft in some regions and firm in others with some reddish coloration with no discharge coming out of it. The patient reported that she had no previous surgeries, no chronic diseases, and no history of smoking. The cyst was small for a long time about ten years ago, but recently, it has grown significantly in size over the last two months. This big mass was not associated with respiratory symptoms or other problems except a scoliosis, which has developed during the growth of the cyst (Figure 1). At presentation, laboratory tests revealed white blood cell (WBC) 12,300/mm³, red blood cell (RBC) 5.29×10⁶/mm³, hemoglobin (Hgb) 13.6 g/dL, platelet (Plt) count 33310³/mL, erythrocyte sedimentation rate (ESR) 20 mm, C-reactive protein (CRP) 3.8 mg/L, Urea 37 mg/dL, Creatinine 0.9 mg/dL, lactate dehydrogenase (LDH) 199 U/L.

Computed tomography (CT) revealed a subcutaneous huge mass 25.0 × 20.0 × 9.0 cm extended from cervical vertebrae level into upper lumbar vertebrae with infiltration into latissimus dorsi muscles, extension until erector spinae muscles and infiltration into the intercostal muscles (Figure 2).

Surgery with the intent of wide and complete excision was performed, but the mass was extended into the deep muscles and the complete excision was difficult to obtain (Figure 3). The excised specimen was sent to the pathology department. The gross inspection of the specimens revealed fragmented white-gray soft to firm tissue, which measured in aggregate 17.0 × 11.0 × 4.0 cm. The surface of some fragments were irregular. In general, infiltration of variably differentiated malignant squamous cells with occasional central keratin pearls and intervening desmoplastic stroma was seen in the hematoxylin and eosin (H&E) stained sections taken from specimen. Furthermore, segments of fibrous wall covered by regular squamous epithelium and hyperkeratosis also detected in the specimen. Finally, the diagnosis of malignant transformation of epidermoid cyst was reported (Figure 4 and Figure 5).

Epidermoid cysts are a common type of cutaneous cyst that can occur at any age although they are frequently found in adulthood and are usually diagnosed later in life. The lesions can present on the skin and in many visceral organs [1]. They may be solitary or multiple lesions also and they can be congenital or acquired. Epidermoid cysts are found just under the surface of the skin originating from the follicular infundibulum and are usually filled with keratin, cholesterol clefts, or degenerated blood components. The lining of the cyst produces keratin [1]. Although these cysts are recognized as benign lesions, a malignant transformation to SCC and BCC can occur (~1%) [2]. Epidermoid cysts usually remain asymptomatic although a rupture of the cyst lining may happen and cause an inflammation of the cyst [3]. When suspected infected cysts fail to respond to medical management, malignant transformation should be considered. Other symptoms may raise suspicions of this transformation including rapid growth, pain, ulceration, and persistent drainage of the cyst [1].

Physical examination, radiological examination, and biopsy are useful procedures for diagnosis although pathological examination mostly confirms diagnosis. Radiological studies including ultrasound, CT, and magnetic resonance imaging (MRI) should be done [4]. The primary treatment for a malignant EC is wide excision with adequate margins [5]. When the cyst is actively inflamed, excision should be delayed because of a high risk of infection. Following the surgery, complications such as inflammation and wound dehiscence may occur, but this did not happen in our case.

While small cysts may be treated by carbon dioxide (CO₂)- or erbium-yttrium aluminum garnet (YAG)-laser, larger cysts need a surgical approach with complete removal of the lesions. Liu et al. [6] demonstrated that CO₂ laser fenestration-assisted procedure is an effective option for the treatment of epidermal cysts and it can achieve good aesthetic results with a low recurrence rate.

In this case, it was difficult to obtain clear margins of tumor by surgery so that the patient has received radiotherapy after surgery. Kim et al. [4] analyzed 432 cases of epidermoid cyst in 398 patients who underwent complete excision and biopsy, according patient age, gender, and lesion location. About 65% of cases were on the face, 10.9% on the trunk with 7.9% on the back, 7.9% on the scalp while 4.3% on lower extremities. The cases occurred at a men-to-women ratio of about 3:2.

Although cutaneous cysts usually occur more frequently in men than women, the rate has been variously reported. Dutta et al. [7] reported a male-to-female ratio of 4.6:1 and Jham et al. [8] reported a ratio of 3:1. In Korea, Han and Kim [9] reported a ratio of 1.8:1 and Heo and Oh [10] reported a ratio of 2.8:1.

There are some suggestions about the mechanism behind malignant transformation of ECs although they are still theories; chronic inflammation or infection of the cysts, some factors like trauma, immunosuppression, human papillomavirus, and actinic damage [8]. Histopathological examination should be performed to confirm the diagnosis and to be sure about complete excision. A differential diagnosis of an epidermoid cyst can be lipomas, milia, furuncles, melanomas, etc. Frank et al. [3] reported that the most common site of occurrence of epidermal inclusion cysts was the head and neck (54.8%) in a review of 41 cases of SCC arising from cutaneous epidermal cysts.

Cyst size varied significantly with the largest diameter of cyst of 20 cm. Men were more often affected (69%). The most common presenting symptoms were rapid enlargement and pain.

Malignant transformation of epidermoid cysts is possible although it is uncommon. These cysts can cause functional and cosmetic impairment, so it is better to be treated as early as possible.