There are several types of skin cancer. Basal Cell, Squamous Cell and Merkel Cell are the three forms of non-melanoma skin cancer and account for 99% of all cases of skin cancer.
Melanoma and Ocular (Uveal) Melanoma are rarer, but more dangerous forms of skin cancer.
Precancerous conditions of the skin have the potential to develop into non-melanoma skin cancer. The most common precancerous conditions of the skin are actinic keratosis and Bowen’s disease.
BASAL CELL CARCINOMA
Basal cell carcinoma (BCC), the most common type of skin cancer, begins in the basal cells in the deepest layer of skin. BCC can develop anywhere, though it is most commonly found in sun exposed areas. It is possible to have more than one BCC.
It is rare but possible for BCC to spread, or metastasize – it is estimated that ~1% of BCCs can be classified as advanced BCC. (Mohan SV & Chang ALS. Curr Derm Rep 2014;3:40–5)
There are several subtypes of BCC:
The most common subtype of BCC is nodular BCC, which often appears as a raised lesion with blood vessels on top. It usually appears on the face.
The second most common subtype is superficial BCC, which takes the form of a red, scaly patch. It often develops on the torso and limbs.
In the deeper layers of skin, infiltrative BCC can occur. Infiltrative BBC often occurs in the neck and head regions, and takes the appearance of scar tissue.
Morpheaform or sclerosing BCC usually occurs in the neck and head regions, and takes the appearance of a flat, firm lesion lacking a defined border.
Source: Canadian Cancer Society, “Basal Cell Carcinoma“
Melanoma begins as a malignant tumour in the melanocytes, which are the cells that produce melanin or pigment. As a malignant cancer, melanoma can metastasize to other parts of the body. There are several subtypes of melanoma, including cutaneous, mucosal, and ocular melanoma.
There are three different types of melanoma:
There are four different types of cutaneous melanoma, which are determined by microscopic examination of a biopsy sample.
- Superficial Spreading Melanoma counts for approximately 70% of melanomas of the skin. Superficial spreading melanoma usually develops from an atypical mole and can be found anywhere on the body.
- Nodular melanoma makes up about 10-15% of melanomas. Nodular melanoma starts growing down into the skin and spreading quickly.
- Lentigo maligna melanoma makes up about 10-15% of melanomas. Lentigo maligna melanoma is most often seen on skin that has been exposed to the sun. These spots are often large.
- Acral lentiginous melanoma occurs as often in African Americans as in Caucasians. Acral lentiginous melanoma grows and spreads rapidly.
NOTE: ATYPICAL OR AMELANOTIC MELANOMA
About 2% of all melanomas are amelanotic. Amelanotic melanoma is the subtype most often reported as simulating other cutaneous lesions, but even pigmented melanomas are commonly misdiagnosed—especially as melanocytic naevus, basal cell carcinoma, seborrhoeic keratosis or lentigo.
Any changing or atypical mole or non-healing skin lesion should be referred urgently to a dermatologist or to a surgeon with a special interest in pigmented lesions. Early detection of malignant melanoma is essential since survival prospects are strongly related to tumour (Breslow) thickness at the time of diagnosis. The Breslow thickness, measured on histological examination, is the distance between the overlying epidermal granular layer and the deepest invasive area of the primary lesion.
Mucosal melanoma develops in the lining of the respiratory, gastrointestinal, and genitourinary tracts. It is a rare form of melanoma, making up only about 1% of melanoma cases and is often diagnosed at an advanced stage in the elderly. Approximately 50% of mucosal melanomas begin in the head and neck region, 25% begin in the ano-rectal region, and 20% begin in the female genital tract. The remaining 5% occur in the esophagus, gallbladder, bowel, conjunctiva, and urethra.
Ocular melanoma is rare, affecting approximately five in a million people. While it represents only 5% of melanomas, ocular melanoma is rapid and aggressive, accounting for 9% of melanoma deaths.
MERKEL CELL CARCINOMA
Merkel Cell Carcinoma (MCC) is a rare non-melanoma skin cancer. It can develop in the merkel cells, which are found in the deepest areas of the epidermis and hair follicles. Merkel cells are related to nerve function and production of hormones. MCC generally spreads quickly, and develops in areas often exposed to the sun (head, neck, arms, and legs), but can occur anywhere on the body. Once the cancer starts to metastasize, or spread, to other parts of the body, it becomes metastatic MCC. MCC is sometimes referred to as neuroendocrine skin cancer or trabecular carcinoma.
MCC generally manifests in a non-painful firm, raised bump on the skin, which may be red or purple in colour. As MCC spreads more bumps may appear nearby, and swelling may occur in the lymph nodes.
Source: Canadian Cancer Society, “Merkel Cell Carcinoma“.
SQUAMOUS CELL CARCINOMA
Squamous cell carcinoma (SCC), which begins in the keratinocyte cells, is the second most common skin cancer. While SCC usually develops in areas that have been exposed to the sun, it can also manifest in burn or wound sites.
SCC is capable of spreading from the surface to deeper layers of skin, lymph nodes or organs. The annual incidence of metastasis of CSCC is approximately 4%. (Burton et al. Am J Clin Dermatol. 2016;17:491-508.)
There are two subtypes of SCC, Adenoid SCC and Desmoplastic SCC, which may have a higher chance of recurrence. Both subtypes often occur on the head or neck, and Adenoid SCC appears as a nude, brown, pink or red nodule.
Source: Canadian Cancer Society, “Squamous Cell Carcinoma“