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A 77-year-old Caucasian man presents with an epidermoid cyst on his scalp, in the left parietal area. He tells you he has had the cyst for many years and it always seemed to remain the same. He is concerned because recently, its size has increased significantly.

He reports that his medical history includes bladder tumor, malignant tumor of the left ureter, malignant prostate cancer, and vitamin D deficiency.

Based on the cyst's rapid growth and the clinical history of malignancies, clinicians determine that the mass should be excised and sent to pathology for examination, a procedure that is completed without complications.

Surprisingly, the pathology report identifies a moderately differentiated (G2) squamous cell carcinoma, 2.1 × 2.1 cm in size, with unclear margins and without lymphovascular invasion.

At first consultation, the patient is reluctant to proceed with any further interventions due to his other preexisting medical conditions. When he returns for a 4-week follow-up visit, accompanied by his daughter, clinicians explain the two treatment options:

• The first involves a wide excision of the tumor to ensure clear margins with a small possibility of follow-up radiation therapy

• The second is radiation therapy as the primary treatment

Treatment Course

After some consideration, the patient decides to go ahead with wide excision of the tumor. The pathology report on the specimen retrieved during the wide excision procedure shows clear margins and no evidence of any residual cancerous cells. Surgeons close the resulting defect, which is 4.5 × 5 cm in size, using a modified pinwheel design of three fasciocutaneous flaps.

The patient recovers well without any major complications or additional adjunctive chemotherapy or radiation treatments, and the incisions heal nicely.

Discussion

Clinicians reporting this case¹ of malignant transformation of an epidermoid cyst note that while such malignancies are rare, vigilance and having a low threshold for excision and of specimens are crucial to allow early diagnosis and treatment.

Epidermoid cysts – sometimes referred to as sebaceous cysts – are the most common benign skin lesions, representing about 85-90% of all surgically removed cysts.²

These generally asymptomatic and painless soft lesions can occur anywhere on the body, although they frequently develop on the face, scalp, neck, and trunk.³ Epidermal cysts present as firm skin-colored dermal nodules, usually filled with keratinous or sebaceous materials.

of epidermoid cysts into squamous cell carcinoma is rare,^4-6 ranging in incidence from 0.033% to 9.2% in the English language literature.^5,7-9

Reports vary widely in terms of sample size and target population, the authors explained: an analysis of 9,000 routine examinations reported the lowest incidence at 0.033%,⁷ while a sample of 119 suspicious lesions noted the highest incidence of 9.2%.⁸ Only about 12 cases of malignant transformation of epidermoid cysts to squamous cell carcinoma have been reported.

While the cause of malignant transformation is not well understood, it has been attributed to prolonged chronic inflammation in long-standing lesions.²

Despite the fact that epidermoid cysts are typically benign, and malignant transformation is rare, clinicians reporting this case suggest the possibility of malignancy should be considered in the diagnosis of suspicious lesions.

Red flag features of high-risk epidermoid cysts are the following:

• Recurrent lesions

• Rapid growth in size

• Rapid symptom progression of symptoms¹⁰

• Size larger than 2.0 cm in diameter

• Heterogeneous mixture of cyst content¹¹

Highly suspicious lesions that are well confined should be surgically removed and their pathology examined carefully to identify any of the red flag features.^3,12 In patients with preexisting malignancy, clinicians should consider the potential for increased risk for malignant transformation despite a paucity of supporting data, the case authors suggest.

Once the transformation has occurred and is confirmed,¹⁰ consideration of treatment options will depend on the tumor type.

The authors note that despite incomplete understanding of the underlying etiology, the true incidence of malignant transformations of epidermoid cysts has been steadily increasing.

In addition to surgical resection, adjunctive treatments such as chemotherapy and radiotherapy may be beneficial, and have been associated with increased postoperative survival times.^13-15

Effective communication between the pathologist and the surgeon can help guide adequate surgical removal as well as any reconstructive procedures that might be required following excision of the lesion.¹⁶

The existing body of research is not yet sufficient to determine the clear relationship between the presence of malignancy, the possibility of concurrent cancer therapy involvement, and the risk of malignant transformation from epidermoid cyst to squamous cell carcinoma. Nevertheless, the case authors point out that the lack of sufficient data does not equal absence of a relationship.

References

1. Faltaous AA, et al: A rare transformation of epidermoid cyst into squamous cell carcinoma: A case report with literature review. Am J Case Rep 2019; 20: 1141-1143.

2. Murray JC, et al: Benign skin tumors: Clinical aspects and histopathology. In: Georgiade GS, Riefkohl R, Levin LS (eds.), Plastic, maxillofacial, and reconstructive surgery, Baltimore, Williams & Wilkins, 1997; 138–149.

3. Sabhlok S, et al: Congenital giant keratinous cyst mimicking lipoma: Case report and review. Indian J Dermatol 2015; 60(6): 637.

4. López-Ríos F, et al: Squamous cell carcinoma arising in a cutaneous epidermal cyst. Am J Dermatopathol 1999; 21(2): 174–177.

5. Bauer BS, Lewis VL: Carcinoma arising in sebaceous and epidermoid cysts. Ann Plast Surg 1980; 5(3): 222–224.

6. Yaffe HS: Squamous cell carcinoma arising in an epidermal cyst. Arch Dermatol 1982; 118(12): 961.

7. Bishop EL: Epidermoid carcinoma in sebaceous cysts. Ann Surg 1931; 93(1): 109–112.

8. Collins DC: Carcinoma originating in sebaceous cysts. Can Med Assoc J 1936; 35(4): 370–372.

9. Amaral ALMP, et al: Proliferating pilar (trichilemmal) cyst. Report of two cases, one with carcinomatous transformation and one with distant metastases. Arch Pathol Lab Med 1984; 108(10): 808–810.

10. Vellutini EAS, et al: Malignant transformation of intracranial epidermoid cyst. Br J Neurosurg 2013; 28(4): 507–509.

11. Apollos JR, et al: Routine histological examination of epidermoid cysts; to send or not to send? Ann Med Surg 2017; 13: 24–28.

12. Welch JW: Carcinoma arising in sebaceous cysts. Arch Surg 1958; 76(1): 128–132.

13. Nakao Y, et al: Malignant transformation 20 years after partial removal of intracranial epidermoid cyst. Neurol Med Chir (Tokyo) 2010; 50(3): 236–239.

14. Chon K-H, et al: Malignant transformation of an epidermoid cyst in the cerebellopontine angle. J Korean Neurosurg Soc 2012; 52(2): 148–151.

15. Tamura K, et al: Malignant transformation eight years after removal of a benign epidermoid cyst: A case report. J Neurooncol 2006; 79(1): 67–72.

16. Costa D, et al: Scalp rotation flap for reconstruction of complex soft tissue defects. J Neurol Surg B Skull Base 2015; 77(01): 32–37.

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