How this class of oral targeted therapy works and what to expect
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Almost every basal cell carcinoma (BCC) is cured by a single surgery or a course of radiation. A small number are not: the tumor may be too large or deep, wrapped around a nerve, destroying cartilage or bone, back for the third or fourth time, or in a spot on the face where removing it would cause unacceptable damage. A very few spread to lymph nodes or beyond. Doctors call these tumors advanced BCC.
When surgery and radiation are no longer good options, the first systemic (whole-body) treatment for advanced BCC is usually a hedgehog pathway inhibitor — an oral targeted drug taken as a capsule once a day at home. Two are approved: vismodegib (Erivedge) and sonidegib (Odomzo). This article explains the pathway they block, how well they work, and what living with the treatment involves.
The "hedgehog" signaling pathway is a chain of molecules inside cells that carries a "grow and divide" message. It is intensely busy before birth, when it helps build skin, hair, bone, and other tissues. In adults it is mostly switched off, kept in reserve for repair and for the normal upkeep of hair follicles, taste buds, and a few other tissues.
In roughly nine out of ten basal cell carcinomas, a genetic change jams this pathway in the "on" position. Most often the tumor has lost a gene called PTCH1, which normally acts as the pathway's brake. Less often, a gene called SMO is altered so that it stays active. Either way, the cell receives a nonstop growth signal, and a BCC is the result.
This is why the hedgehog pathway is such a useful target in BCC: the same faulty signal is driving the large majority of these tumors, so a drug that interrupts it can work across many different patients. The same pathway is overactive in nearly all the tumors of people with Gorlin syndrome, an inherited condition that causes many BCCs over a lifetime.
Both vismodegib and sonidegib block the same protein — SMO (smoothened), which sits in the middle of the hedgehog pathway and passes the growth signal along. With SMO blocked, the signal is cut off:
Vismodegib is taken as a 150 mg capsule once a day; sonidegib as a 200 mg capsule once a day. There are no infusions and no hospital stays — treatment happens at home, with regular clinic visits to check on progress.
Both drugs were approved on the strength of clinical trials in people with advanced BCC that could not be treated by surgery or radiation.
In the pivotal ERIVANCE study, about 43% of locally advanced tumors and 30% of metastatic tumors shrank significantly, and roughly one in five locally advanced tumors could no longer be seen on examination. The larger STEVIE study, which followed more than 1,200 patients treated in routine practice, found a similar level of benefit and no unexpected safety problems.
Vismodegib is approved for adults with metastatic BCC, and for locally advanced BCC that has come back after surgery or that is not suitable for surgery or radiation.
In the BOLT study, roughly four to six of every ten locally advanced tumors responded at the approved 200 mg dose, depending on how response was measured. Longer follow-up showed responses lasting a median of about two years. Sonidegib is approved for adults with locally advanced BCC that has recurred after surgery or radiation, or who are not candidates for those treatments; it is not approved for metastatic disease.
The two drugs have never been compared head-to-head. The choice between them comes down to availability, the exact type of advanced disease, other medical conditions, and the expected side-effect profile.
Shrinkage usually begins in the first one to three months, but the fullest response can take six months to a year. Your team will track progress with photographs, skin exams, and — if there is disease deeper in the body — periodic scans.
Nearly everyone develops side effects, because the drug also dials down the hedgehog pathway's normal jobs in muscle, hair follicles, and taste buds. Muscle cramps, changes or loss of taste, hair thinning, weight loss, and fatigue are the common ones. They are rarely dangerous, but over months they can be wearing — and they, not the cancer, are the usual reason people pause or stop. Many of these effects can be eased with supportive care or planned treatment breaks: see how the side effects of hedgehog inhibitors are managed.
Both drugs cause severe birth defects. Patients who can become pregnant must use reliable contraception during treatment and for a period after the last dose (longer for vismodegib), and pregnancy must be ruled out before starting. Male patients should use condoms with a pregnant or potentially pregnant partner. Neither patients nor, for vismodegib, male patients should donate blood during treatment or for a set time afterward. Your team will go through the exact timelines with you.
Many people stay on treatment for as long as it is helping and the side effects are manageable. In some people the tumor eventually adapts and starts growing again after months or years — the pathway finds a route around the blocked SMO protein. If that happens, options include immunotherapy or a clinical trial.
A hedgehog inhibitor is occasionally given for a few months to shrink a tumor first, so that surgery can be smaller and spare more healthy tissue — an approach called neoadjuvant therapy.
Hedgehog pathway inhibitors gave advanced BCC its first effective drug treatment. By blocking the single faulty signal that drives most basal cell carcinomas, vismodegib and sonidegib can shrink tumors that surgery and radiation cannot reach, and for many people they hold the disease in check for years.
They are demanding drugs to take, and side effects shape the experience as much as the response does. Going in with realistic expectations — steady control rather than a quick cure, with a plan for managing side effects — makes the treatment easier to stay with.
Disclaimer: This article is for educational purposes only and not a substitute for professional medical advice. Always consult a qualified dermatologist or oncologist about your personal diagnosis and treatment plan.
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