What basal cell carcinoma looks like, why it rarely spreads yet still needs treatment, how doctors treat it, and the odds of getting another.
Basal cell carcinoma, usually shortened to BCC, is the most common cancer in humans. About 8 of every 10 skin cancers are BCCs, according to the American Cancer Society, and the Skin Cancer Foundation estimates that 3.6 million cases are diagnosed in the United States each year. It starts in basal cells, which sit at the bottom of the epidermis, the thin outer layer of skin.
Years of ultraviolet light from the sun or tanning beds cause most BCCs. The face, head, neck, and arms are the usual sites.
BCC has several faces, and many people mistake one for a pimple or a scrape that won't heal. The Skin Cancer Foundation and DermNet describe these common appearances:
In people with brown or Black skin, about half of BCCs are pigmented. They look brown or black and can pass for an ordinary mole.
When a pathologist examines the biopsy, the report usually names a growth pattern. The pattern matters because it predicts how far the tumor's roots extend beyond what the eye can see.
Nodular BCC is the classic pearly bump and the most common type on the face. It tends to grow as a compact ball, so its edges are fairly easy for a surgeon to define. Superficial BCC spreads sideways along the top of the skin as a thin, scaly plaque with a fine rolled border.
Infiltrative and morpheaform (also spelled morphoeic, or called sclerosing) BCCs behave differently. They send thin strands of tumor cells out through the dermis, the thicker layer under the surface, like roots through soil. On the skin they may look like nothing more than a waxy scar with blurry borders. DermNet describes these tumors as having wide and deep extension that can't be seen from the surface.
BCC grows slowly, and spread to lymph nodes or distant organs is very rare.
The risk with BCC is local. An untreated tumor keeps enlarging and can destroy the skin, cartilage, and even bone around it. On the nose, eyelid, or ear, a few extra millimeters of growth can turn a small repair into a complex reconstruction. Delay also raises the chance that the tumor will come back after treatment.
Doctors seldom assign BCC a formal stage, because treatment almost always cures it before it could spread. Doctors sort tumors into low-risk and high-risk groups for recurrence instead. The American Cancer Society lists these high-risk features:
Surgery cures the great majority of BCCs. For small, low-risk tumors, a doctor may scrape the tumor away with a curette, a spoon-shaped instrument, and then cauterize the base with an electric needle. This is called curettage and electrodesiccation. Standard excision cuts out the tumor with a margin of normal skin, and a pathologist checks the edges afterward.
Mohs surgery is the usual choice for high-risk BCCs, including those on the central face, those with blurry edges, and those that have recurred. The surgeon removes the tumor one thin layer at a time and examines each layer under the microscope while you wait, stopping only when no cancer remains. This approach gives the highest cure rate and spares the most healthy skin.
Some superficial, low-risk BCCs can be treated without cutting. Options include imiquimod cream, fluorouracil cream, photodynamic therapy (a light-activated drug treatment), and cryotherapy (freezing). Radiation therapy serves people who cannot have surgery, and doctors sometimes choose it for tumors on the eyelid, nose, or ear.
A small number of BCCs grow too large for surgery or radiation, or spread. For these, doctors can prescribe vismodegib (Erivedge) or sonidegib (Odomzo), pills that block the hedgehog pathway, a growth signal that drives most BCCs. If those drugs stop working or cause intolerable side effects, the immunotherapy drug cemiplimab (Libtayo), given through a vein, is approved as the next option.
According to the American Cancer Society, the chance that a treated BCC returns ranges from less than 5% after Mohs surgery to 15% or higher after some non-surgical treatments.
A new BCC somewhere else is far more likely than a recurrence. DermNet reports that about 50% of people with a BCC develop a second one within 3 years.
For these reasons, dermatologists generally recommend a full skin exam at least once a year after a BCC, along with regular self-checks and daily sun protection. In the ONTRAC trial (Chen and colleagues, New England Journal of Medicine, 2015), 386 Australian adults who had already had at least 2 skin cancers took 500 mg of nicotinamide, a form of vitamin B3, or a placebo twice a day for a year. The nicotinamide group developed 23% fewer new basal and squamous cell cancers during that year.
