Differences Between Basal Cell Carcinoma and Actinic Keratosis
What is basal cell carcinoma?
Basal cell carcinoma (BCC) is the most common type of skin cancer, accounting for 80-90% of all skin cancers [1]. It originates from the basal layer of the epidermis, which is the layer of cells at the bottom of the outer layer of the skin [2]. BCC is most common in fair-skinned adults over 50 years of age, and is very prevalent in white populations, with a lifetime risk of 30% [3, 4].
The development of BCC is not fully understood and is likely an interplay of genetic and environmental factors. However, it is known that exposure to ultraviolet (UV) light is the primary causative agent. The radiation, primarily short-wavelength UVB radiation, damages the DNA in the basal cells, leading to growth of damaged (mutated) cells undergoing malignant transformation.
How is basal cell carcinoma diagnosed and treated?
Diagnosis of BCC relies on clinical examination and a skin biopsy. BCC usually presents as a growth or a bump on the skin that is shiny, skin-coloured or pink. BCC can also sometimes be pigmented (coloured dark), resembling melanoma, or translucent, with blood vessels visible underneath the lesion [2].
A skin biopsy is essential to confirm the diagnosis and characterise the tumour [5]. This is an in-office procedure done under local anaesthesia, where a small sample of the lesion and/or surrounding skin is taken. Additionally, the lesion can be looked at using modern imaging techniques such as optical coherence tomography or confocal laser microscopy [6, 7].
What is the treatment and prognosis for basal cell carcinoma?
Fortunately, BCC is very manageable due to the fact that its metastatic potential is low, meaning that the cancer does not usually spread. Therefore, the treatment focuses on local management of the lesion and involves a complete removal of the lesion.
Mohs surgery, a type of approach where the skin surrounding the tumour is examined under the microscope for presence of cancer cells during the surgery, is commonly used. Alternatively, the cancer can be treated with cryotherapy (freezing with liquid nitrogen), electrocautery ("burning off" the lesion with a tool using electrical current). Topical chemotherapy can also be used, as well as radiotherapy to the tumour site [1, 2].
In the case of the tumour metastasising, targeted therapeutics are used, such as vismodegib and sonidegib [8]. Systemic cytotoxic chemotherapy may be indicated in very advanced and difficult to treat cases.
Consequently, the prognosis for BCC is very good. Following removal, 95% of patients do not experience recurrence.
What is actinic keratosis?
Actinic keratosis, also known as solar keratosis, is a pre-cancerous growth that presents as a rough patch of skin and is caused by UV exposure. It may be pink or red, but can also be flesh-coloured or pigmented.
This condition is very common and is caused by chronic exposure to ultraviolet (UV) light found in sunlight [2, 9] - about 75% of the time it appears on body parts chronically exposed to sunlight such as the arms, scalp, ears and face.
Risk factors for actinic keratosis include older age, male sex, having fair skin, family history of actinic keratosis or other skin conditions, immune system dysfunctions, and, most importantly, chronic unprotected exposure to sunlight [2, 9].
How is actinic keratosis treated?
Treatment options for actinic keratosis are divided into lesion-directed treatments that target individual spots and field-directed treatments that treat a wide area. Additionally, between 15 and 63% of actinic keratosis may spontaneously regress (the body resolves the condition and restores healthy skin in the damaged area).
Lesion-directed treatment options include cryosurgery (where the lesion is frozen with liquid nitrogen), curettage (shaving off the damaged skin), and surgical removal. Field-directed treatments include dermabrasion (a procedure where the outer layer of the skin is removed), laser therapy, chemical peel, photodynamic therapy, and topical medications, such as 5-fluorouracil, imiquimod, diclofenac sodium, and ingenol mebutate [10, 2, 9].
The prognosis of actinic keratosis is generally good and the current treatments are effective at removing the damaged cells and resurfacing healthy skin. However, actinic keratosis is a pre-cancerous condition, meaning that the damaged cells have potential to replicate and start forming a cancerous tumour.
Some cases of actinic keratosis progress to squamous cell carcinoma, which is a type of skin cancer originating from the outer cells of the skin. Data on actinic keratosis vary in concluding what is the risk of this progression, with numbers between 1% and 20% reported to progress to squamous cell carcinoma.
What are the differences?
To summarise, basal cell carcinoma (BCC) and actinic keratosis (AK) are both skin conditions that are primarily caused by exposure to ultraviolet (UV) radiation from sunlight. However, they differ in their nature, progression, and associated risks.
BCC is a type of skin cancer that originates from the basal (bottom) layer of the epidermis. It is the most common type of skin cancer, however it is very manageable as it grows slowly and typically does not metastasise. However, in rare cases, metastasis and spreading are possible [11]. BCC is primarily treated with surgery aiming to remove the whole tumour, and surgery is very successful at minimising recurrence.
On the other hand, AK is a precancerous skin lesion that can sometimes turn into skin cancer, specifically squamous cell carcinoma (SCC), not BCC. It is also linked to exposure to sunlight, however the cells damaged are in the top (squamous) layer of the skin. The risk of AK progressing to SCC varies widely, estimated between 1% and 20%.
The diagnosis of both conditions relies on dermatological examination and a skin biopsy. In terms of treatment, the goal is to remove the damaged and/or cancerous cells early so that the metastatic potential is minimised.
Finally, it is very important to protect yourself from sunlight by using sunscreen and covering exposed skin if possible. It is also very important to visit the dermatologist regularly, particularly if you are at-risk (for example have a fair skin, are over 50 years old and live in an area with lots of sunlight) and get all suspicious moles and other blemishes checked out.
