Basal cell carcinoma in skin of colour

Author: Rajan Ramji, final year medical student, Auckland, New Zealand. DermNet New Zealand Editor in Chief: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy editor: Gus Mitchell. October 2017.

What is a basal cell carcinoma?

A basal cell carcinoma (BCC) is a keratinocytic or non–melanoma skin cancer formed by uncontrolled growth and replication of basal cells in the lower levels of the epidermis. They are sometimes referred to as rodent ulcers or basaliomas.

What is skin of colour?

Skin of colour is a subjective term referring to natural skin pigmentation ‘darker’ than white (ie, brown or black skin). When compared against a graded assessment of skin colour types such as the Fitzpatrick scale, ‘skin of colour’ may refer to skin classified as type IV or higher [1]. In some contexts, ‘skin of colour’ is also used to describe the skin type of a non–white ethnic group including those of African, Asian, South American, Pacific Island, Maori, Middle Eastern, and Hispanic descent [1].

Who gets basal cell carcinoma?

BCCs are among the most commonly diagnosed cancers worldwide. BCC accounts for 65–75% of skin cancers [2]. BCC is the most common form of skin cancer seen in Caucasians, Asians, and Hispanics. It is the second most common form of skin cancer seen in African Americans and Asian Indians [3].  

Incidence data

Reported incidence rates of BCC tend to vary across different studies and time periods, although incidence rates per 100,000 across the last 50 years have been:

Global incidence rates of BCC are increasing, and this trend is significantly more prominent in white skinned people, particularly in older age groups and in women [5,7]. Most diagnoses occur at over 50 years of age and peak at around 70–80 years of age in both men and women, regardless of skin colour [5]. 

Risk factors for BCC

BCC is more common in individuals with:

Ultraviolet radiation exposure (sunlight) is a much more significant risk factor for BCC in white–skinned people [3]. However, while sunlight is generally less of a risk factor in skin of colour, susceptibility to BCC varies between individuals with the same skin type depending on their ethnic origins [4].

What causes basal cell carcinoma?

BCC is thought to begin from an uncontrolled proliferation of basal cells in the skin following an abnormal genetic transformation, usually as a result of sun exposure as UV light damaging and mutating DNA [5]. In addition, UV radiation suppresses the ability of the immune system to detect and destroy tumour cells. In darker skin, a higher content of UV light–absorbing melanin protects the DNA from mutation and damage.  

What are the clinical features of basal cell carcinomas? 

Regardless of skin colour, BCCs can occur anywhere on the skin. The most common sites are the face and ears, neck, shoulders, and back. There are various subtypes of BCC.

Nodulocystic BCC

These are small and slow growing translucent lesions with rolled edges.

Superficial BCC

The most common type of BCC found in younger adults.

Morphoeic BCC

Also known as morpheaform or sclerosing BCC. 

Basosquamous BCC

Also known as mixed basal cell carcinoma (BCC) and squamous cell carcinoma (SCC).

Adenoid BCC

A rare histological variant of BCC.

Fibroepithelial tumour of Pinkus

A warty plaque, usually found on the trunk.

What are the clinical features of basal cell carcinoma in skin of colour?

Diagnosis of basal cell carcinoma in skin of colour can be difficult due to their rarity and pigmentation. More than 50% of BCCs found in skin of colour are pigmented with ‘pearly’ brown or black appearance.

Nodular BCCs are the predominate subtype found, while morphoeic BCCs are rare. Adenoid BCC is more common than in Caucasians.  

What are the complications of basal cell carcinoma?

Complications of BCCs may include: 

Recurrence of BCC

BCCs have an estimated 3–10% 5–year recurrence rate depending on whether the treated lesion is a primary BCC or itself a recurrence. Most recurrences are evident 4–12 months after treatment. Recurrence is more likely with:

The type of treatment received on a BCC can also influence recurrence rates. Higher recurrence rates (~7–10%) may be seen with all treatment methods except Mohs micrographic surgery (~1%) [8].

Development of new BCCs

There is a significantly increased risk of developing new BCCs after a previous one. Estimates from various studies have suggested a 3–year cumulative risk of between 30–77% for new BCC formation. Associated factors for new BCC formation may include:

Advanced BCC

Advanced BCCs are often a result of neglect as BCCs are very slow growing tumours, often taking months to years to reach this stage. They may be several centimetres in diameter. They may infiltrate tissues below the skin and are very difficult to treat surgically.

Metastatic BCC

Metastatic or invasive BCCs are rare, with an estimated occurrence rate of 0.03–0.55%. The primary BCC is often large, neglected or recurrent, located on the head and neck region. It may arise in sites exposed to ionising radiation or ones that have had multiple prior treatments. Metastatic BCCs can be fatal.

How is basal cell carcinoma diagnosed?

BCCs are diagnosed by their typical appearance clinically and on examination using a dermatoscope [3]. The diagnosis is confirmed by incision or excisional biopsy.

Staging BCCs

In patients with advanced BCCs, it may be important to determine the depth of tumour invasion and the spread to surrounding tissue. The Union for International Cancer Control (UICC) 8th edition staging system for cutaneous carcinomas (skin cancers) is a commonly used system.

Tumour staging for cutaneous carcinomas

TX: Primary tumour cannot be assessed

T0: No evidence of primary tumour

Tis: Carcinoma in situ

T1: Tumour ≤ 2 cm without high–risk features

T2: Tumour > 2–4 cm

T3: Tumour with invasion of maxilla, mandible, orbit or temporal bone

T4a: Tumour with gross cortical bone/marrow invasion

T4b: Tumor with skull base or axial skeleton invasion including foraminal involvement and/or vertebral foramen involvement to the epidural space 

Nodal staging for cutaneous carcinomas (non–head and neck)

NX: Regional lymph nodes cannot be assessed

N0: No regional lymph node metastasis

N1: Metastasis in one local lymph node ≤ 3cm

N2: Metastasis in a single ipsilateral lymph node > 3 to ≤ 6 cm or in multiple ipsilateral nodes ≤ 6 cm.

N3: Metastasis in lymph node ≥ 6cm

What is the differential diagnosis of basal cell carcinoma?

There are several lesions that can be mistaken for a basal cell carcinoma, especially:

Malignant lesions such as cutaneous SCC and melanoma have a peak incidence at the same approximate age (50+ years) as BCC and may be present simultaneously.

What is the treatment for basal cell carcinoma?

Treatment options are the same, regardless of skin colour. Excisional biopsy with a 3–5mm margin is the standard and recommended treatment for most BCCs. 

Smaller margins increase the risk of recurrence. Deeper incisions and more complex wound closure (flap or skin graft) may be required for larger BCCs. The removed specimen is then examined by a pathologist for a final diagnosis and disease staging [9].

Potential side effects of this procedure can include infection, scarring and temporary or permanent loss of sensation due to nerve severing.

Cryotherapy

Cryotherapy is the treatment of a superficial skin lesion by freezing it, usually with liquid nitrogen [9]. It is suitable for small superficial BCCs (≤1cm) on covered areas of trunk and limbs, and not advised to treat BCCs on head, neck and knees.

Complications and side effects of cryotherapy include:

Shave, curettage and electrocautery

Shave, curettage, and electrocautery are superficial forms of surgery. These techniques require local anaesthesia but are quick to perform and do not require sutures [9].

Mohs margin–controlled micrographic excision

Mohs micrographic controlled surgery involves removing skin tissue in successively deeper horizontal sections under local anaesthetic. Each section is examined with a microscope to identify cancerous tissue. Sections are continually removed until no cancerous tissue is identified [10].

Mohs margin–controlled micrographic excision has very high cure rates achieved by trained dermatologists or dermatologic surgeons.

Imiquimod cream

Imiquimod is a topical immune response modifying drug [9,10]. Imiquimod cream is used when surgical removal is inappropriate.

Side effects and complications of imiquimod cream include:

Fluorouracil cream

5–Fluorouracil cream is a topical cytotoxic agent [9,10]. It is used to treat small superficial basal cell carcinomas.

Side effects and complications of 5–Fluorouracil cream include:

Photodynamic therapy

Photodynamic therapy (PDT) refers to a technique in which BCC is treated with a photosensitising chemical, and exposed to light several hours later [9,10].

Side effects and complications of photodynamic therapy include:

Radiotherapy

Radiotherapy or X–ray treatment can be used to treat primary BCCs or as adjunctive treatment if margins are incomplete [9,10]. Radiotherapy is mainly used if surgery is not suitable. It is best avoided in young patients and in people with genetic conditions predisposing to skin cancer. The best cosmetic results are achieved using multiple fractions.

Side effects and complications of radiotherapy include:

What is the treatment for advanced or metastatic basal cell carcinoma?

Advanced or metastatic BCCs require multidisciplinary consultation. A combination of treatments may be used including:

What is the recommended follow-up for basal cell carcinoma?

There are no established guidelines for follow–up to the removal of a basal cell carcinoma. An annual skin check is recommended for anyone who has had a BCC, given an estimated 30–77% cumulative risk of experiencing another one within 3 years. [8–10].

Year–round protection against excessive sun exposure is important in all skin types.

What is the outcome for basal cell carcinoma in skin of colour?

BCCs are very slow growing tumours and unlikely to reach an advanced stage unless significantly neglected.  As long as it has been completely excised, BCC does not recur. However, another may develop elsewhere.

The prognosis is of the rare metastatic BCC is very poor with a median survival time of 8 months following diagnosis [3,10].   

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