Sebaceous carcinoma

Sebaceous carcinoma is a skin cancer of the sebum producing glands. It is predominantly seen in the head and neck region, representing 25% of all reported lesions in this area.[9] The periocular region, which includes the meibomian gland, caruncle, gland of Zeis and eyebrow, is one of the most common sites in which SC is observed.[10] The meibomian gland is a type of sebaceous gland that lines the upper and lower eyelids, and does not contain a follicle. The glands of Zeis contain the individual eyelash.[11] The upper eyelid contains more meibomian glands than the lower eyelid and consequently, SGc is 2-3 times more common in the upper eyelid.[12]

Patients diagnosed with SGc most commonly present with a painless subcutaneous nodule. Other presentations include an irregular mass, pedunculated lesion or diffuse skin thickening.[13] SGc in the periocular region presents as a heterogeneous rapidly growing, pink or yellow colored painless papule.[14]

The cell of origin is usually unknown. Sebaceous gland carcinoma clearly resembles normal sebaceous glands and is thought to arise from them.[1][2] Ultraviolet and ionizing radiation are believed to play some role in the pathogenesis of these neoplasms.[11] There is a strong association between Muir–Torre syndrome.

There has been an association between the development of sebaceous carcinoma with the following: history of irradiation, immunosuppression, and genetic factors.[11]

One possible hypothesis states that stem cells in the hair follicle bulge and suprabasilar layer respond to different environmental stimuli, such as radiation, that may lead to the development of cutaneous tumors.[15] Immunosuppressed individuals and those undergoing radiotherapy are at an increased risk for SGc. There has been some association between SGc and HIV, HPV (human papillomavirus) and mutations in tumor suppressor genes p53 and Rb. Rb mutations are responsible for retinoblastoma.[12][8] Reports have also shown the onset of SGc within the field of irradiation for patients undergoing radiotherapy for retinoblastoma, eczema or cosmetic epilation.[7]

In addition to external factors, genes also appear to play some role in the pathogenesis of this tumor. Extraocular SGc is closely associated with Muir Torre syndrome (MTS), with sebaceous tumors presenting in nearly 1/3 of patients with MTS.[8]

MTS is an autosomal genodermatosis, described as a condition with 2 types of malignancies: one being a sebaceous gland tumor and the other an internal malignancy, a majority of which are colorectal and genitourinary.[5] In 41% of patients with MTS skin lesions appeared either before or during the time of diagnosis of the primary malignancy.[5]

Studies have shown that cancerous lesions in MTS develop as a result of mutations in DNA mismatch repair genes (MMR), which lead to a buildup of unstable microsatellite sequences and replications errors, predisposing one to different malignancies.[10][5] Given that this is an autosomal dominant condition with multiorgan involvement, diagnosis requires a thorough medical history and physical in suspected cases of SGc in order to rule out potential visceral tumors.

A number of SGc associated mutated proteins (B-catenin, p 53, p21, Shh, Androgen receptor, E-cadherin) have been shown to cause dysregulation in cell signaling. This dysregulation is responsible for the invasive growth and metastasis of SGc and identification of specific mutations could help determine patient prognosis and clinical outcomes.[12]

Due to the variable clinical and histological appearance of SGc, this condition is often misdiagnosed. The average delay in diagnosis has been reported to be 1 – 2.9 years from expected onset of the lesion.[14][7]

Patients with ocular sebaceous carcinomas present with nonhealing eyelid tumors that are often misdiagnosed for more common benign conditions such as chalazion or blepharoconjunctivitis. Extraocular SGc appears similarly to skin cancers such as basal cell carcinoma, squamous cell carcinoma and benign lesions such a molluscum contagiosum and pyogenic granuloma.[14] Many tumors also share a histological presentation similar to SGC, such as sebaceous adenomas, basal cell carcinomas (BCC), squamous cell carcinomas (SCC) and clear cell tumors.[11][14] A high level of suspicion is extremely important to prevent treatment delay and increased mortality.[11]

Given the aggressive growth and pagetoid spread of SGC, full thickness biopsy with microscopic examination is required for definitive diagnosis of sebaceous carcinomas.[10] A full thickness biopsy of the eyelid (in suspected periocular SGC) includes the skin, tarsus, and palpebral conjunctiva.[7] Map biopsies, taken from distinct areas of the conjunctiva, are recommended in cases exhibiting pagetoid spread in order to determine extent of disease.[10] Different markers and stains help differentiate sebaceous carcinomas from other cancers. These markers include lipid stains such as oil red O stain and Sudan IV, and immunohistochemical stains.[13]

This type of carcinoma is commonly managed by local resection, cryotherapy, topical chemotherapy, and radiotherapy. Multimodal therapy has been shown to improve both visual prognosis and survival.[3]

The 5-year relative survival rate for SGc is 92.72% and 86.98% for 10 years. SGc is believed to spread through the blood and lymphatic system via three mechanisms: tumor growth, multifocal tumor proliferation and shedding of atypical epithelial cells that subsequently transplant in a distant site.[14]  Common sites of metastasis for periorbital SGc are regional lymph nodes and rarely in the lung, liver, brain or bone.[8] Due to the difficulty associated with promptly diagnosing SGc tumor, the rate of metastasis and recurrence is relatively high.[11] Approximately 10% of patients with poorly or undifferentiated SGc presented with regional lymph node involvement.[14] At the time of diagnosis nearly 25% of tumors will metastasize, in those with metastasizing cancer survival rate decreases to 50% within 5 years.[11] Recurrence rates are higher in ocular vs extraocular tumors, 4-37% and 4-29% respectively. Over time there has been a notable improvement in prognosis in those with SGc, which is most likely attributable to earlier detection and improved treatment modalities.[13]

Notable risk factors include age, gender, and race. In the United States sebaceous is relatively rare, contributing to only 0.7% of all skin cancers.[8] SGc is more prevalent in the Eastern versus Western Hemisphere, contributing to 33% of eyelid malignancies in China vs 1-5.5% in Caucasians.[3][12] However, it is believed the higher incidence of SGc in Asian populations may be due to the lower incidence of other eyelid tumors.[12] Additionally, a higher incidence has been reported in Caucasians, Asians, and Indians.[7] This skin cancer typically occurs in the elderly, with a reported average age of onset in the 60 to early 70s.[10] Different sources have also reported that SGc may be more common within females versus males, but other resources report no difference in incidence.[8]

• Sebaceous adenoma
• Sebaceous hyperplasia
• Sebaceoma
• List of cutaneous neoplasms associated with systemic syndromes