Basal cell carcinoma (BCC) is the most common form of skin cancer, accounting for approximately 80% of non-melanoma skin cancers. Though basal cell carcinomas are rarely life-threatening, it is important to catch them early, as advanced BCCs can cause significant damage and disfigurement by invading surrounding tissues. Unfortunately, BCCs can sometimes be mistaken for benign skin conditions, delaying diagnosis and treatment.
Seborrheic Keratosis
One of the most common mistakes is confusing basal cell carcinoma for seborrheic keratosis. Seborrheic keratoses are noncancerous skin growths that appear in middle age and beyond. Like BCCs, they often first appear as small, waxy bumps on sun-exposed skin. Seborrheic keratoses can vary greatly in size, color, and texture. They can be light tan to brown or even blackish in color. Their surface may be smooth and warty or textured with a “stuck-on” appearance.
While potentially unsightly, seborrheic keratoses are harmless. However, their appearance under a microscope is very similar to certain types of BCC. Even dermatologists may occasionally misdiagnose a basal cell carcinoma as a seborrheic keratosis upon initial inspection. A biopsy is needed for confirmation.
Distinguishing Features
Some key differences that may help distinguish BCCs from seborrheic keratoses without a biopsy include:
- BCCs often have a translucent or pearly quality, while seborrheic keratoses appear more opaque.
- BCC borders tend to be smoother, while seborrheic keratoses have a more textured, “stuck-on” border.
- BCCs may bleed easily if scratched, whereas seborrheic keratoses generally do not.
- BCCs may occasionally itch or feel tender to the touch, while seborrheic keratoses are not painful.
Actinic Keratosis
Another common mistake is confusing BCCs for actinic keratoses. Actinic keratoses, also known as solar keratoses, are rough, scaly patches of skin caused by years of sun exposure. They form most often on the face, lips, ears, back of the hands, forearms, scalp, and neck.
Like BCCs, actinic keratoses occur on sun-damaged skin and have a sandpaper-like feel. They range in color from skin-toned to reddish or brownish. Early on, it may be impossible to distinguish actinic keratoses from BCCs upon visual inspection alone.
Distinguishing Features
There are a few subtle clues that can help tell actinic keratoses and BCCs apart:
- BCCs are often translucent, pearly, or waxy, while actinic keratoses have a more irregular, scaly appearance.
- BCCs usually appear as dome-shaped bumps, whereas actinic keratoses are flatter.
- BCCs have distinct borders and grow slowly, while actinic keratoses have less defined borders and grow more quickly.
- BCCs may occasionally bleed, but actinic keratoses generally do not.
As with seborrheic keratoses, a biopsy is needed to confirm the diagnosis.
Sebaceous Hyperplasia
Sebaceous hyperplasia is a benign skin condition involving enlarged oil glands (sebaceous glands). It usually occurs on the forehead, nose, cheeks, and chin. Sebaceous hyperplasia appears as small yellowish bumps with a central depression or dimple.
Sometimes basal cell carcinomas arising on the face can be mistaken for sebaceous hyperplasia lesions. Both conditions may appear as waxy, translucent papules in sun-exposed areas. As with other lookalikes, a biopsy is required for a definitive diagnosis.
Distinguishing Features
There are subtle differences between sebaceous hyperplasia and BCC:
- Sebaceous hyperplasia papules often have a central dent, while BCCs usually lack this.
- Sebaceous hyperplasia lesions are small, less than 5 mm, while BCCs are often larger.
- Sebaceous hyperplasia are sparse in number, while BCCs more commonly occur in clusters.
- Sebaceous hyperplasia blanch with pressure, but BCCs do not.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is another form of non-melanoma skin cancer that originates from the squamous cells found in the upper layers of the skin. SCC accounts for approximately 20% of skin cancers.
SCCs typically present as scaly red patches, open sores, elevated growths with a central depression, or raised, rough growths called cutaneous horns. They occur most often on sun-exposed areas like the face, ears, neck, hands, and arms. In rare cases, an SCC may resemble a smooth, translucent bump more typical of BCC.
Distinguishing Features
There are a few ways to tell SCCs and BCCs apart:
- SCCs tend to grow faster and are often crusted or ulcerated, unlike BCCs.
- SCCs may bleed easily, form scabs, and then bleed again after the scab falls off.
- SCCs are typically rough and scaly, whereas BCCs are generally smooth.
- SCCs may be painful or tender, but BCCs are usually not painful.
As with other lookalikes, a biopsy confirms the diagnosis between SCC and BCC.
Melanoma
While basal cell carcinomas virtually never metastasize (spread to distant areas), melanoma is the deadliest form of skin cancer due to its ability to metastasize. In very rare cases, melanoma may mimic the appearance of BCC, causing a delay in diagnosis.
Melanoma most often develops from preexisting moles or other pigmented skin growths. They are distinctive in appearance, with variegated shades of brown, black, blue, red, white, or gray. However, amelanotic melanoma lacks this pigmentation, appearing pink or flesh-colored much like a BCC.
Distinguishing Features
Signs that should raise suspicion for amelanotic melanoma rather than BCC include:
- Rapid growth or changes in the skin lesion
- Irregular, poorly defined borders
- Changes in sensation, itching, pain, tenderness
- Larger size, often over 6 mm when diagnosed
- Occurring on mucous membranes like the mouth, anogenital region
Any concerning, rapidly changing skin lesion warrants an immediate biopsy to rule out melanoma.
Benign Cysts
Epidermoid cysts, also known as sebaceous cysts, are benign keratin-filled lumps beneath the skin surface. They develop when skin cells produce too much keratin and form a plug, trapping the keratin inside the cyst. They may appear very similar to basal cell carcinomas.
Other benign cysts such as milia and atheromas can also mimic BCCs. Milia are tiny, pearly white cysts that form when keratin is trapped beneath the surface of the skin. Atheromas contain sebum rather than keratin and appear as firm bumps on the scalp or face.
Distinguishing Features
Cysts like these differ from BCC in a few key ways:
- Cysts often feel doughy rather than firm or hard.
- Cysts are mobile under the skin and can be moved, unlike fixed BCC lesions.
- Cysts lack the prominent blood vessels of many BCCs.
- Cysts are often smaller, with more uniform shape and color.
If a suspected cyst continues to grow or has any features suspicious for BCC, a biopsy should be performed.
Nodular Melanoma
While most melanomas arise from pigmented lesions like moles, nodular melanomas can appear as firm, dome-shaped growths much like BCCs. They are also one of the most aggressive subtypes of melanoma. Nodular melanomas typically appear suddenly as darkly pigmented or reddish-black bumps rather than developing from preexisting moles.
Distinguishing Features
Clues that should raise suspicion for nodular melanoma rather than BCC include:
- Dark black, blue, gray coloration
- Rapid enlargement over weeks to months
- Occurring in unusual locations like the palms, soles, fingertips, toes, or mucous membranes
- Signs like bleeding, itching, or tenderness
Any new bump that grows rapidly warrants an urgent biopsy to rule out nodular melanoma.
When to Seek Medical Care
Basal cell carcinomas can often be difficult to distinguish from benign growths visually. The key is paying attention for any lesions that are persistent, growing, bleeding, or changing in any way. Such lesions warrant evaluation by a dermatologist for a biopsy to confirm the diagnosis.
Be especially wary of firm, translucent, pearly bumps with visible blood vessels on sun-exposed skin. Also be vigilant about any growths with irregular borders, variegated colors, or other signs of melanoma. Catching BCCs and other skin cancers early allows for simpler, less disfiguring treatment.
Conclusion
Basal cell carcinomas have a wide range of benign lookalikes ranging from seborrheic keratoses to cysts. Seborrheic keratoses and actinic keratoses in particular often mimic BCCs. Even benign cysts and more concerning nodular melanomas or squamous cell carcinomas may resemble BCC. Given this broad differential diagnosis, biopsy of any suspicious skin lesion is key for an accurate diagnosis. With early detection, BCCs have a high cure rate with simple excision.