Merkel cell carcinoma (MCC) is extremely rare. About 3,000 people are diagnosed with it each year in the United States, making it roughly 35 times less common than melanoma, which sees about 106,000 new cases annually. With an incidence rate of around 0.7 cases per 100,000 people, most doctors will never encounter it in their careers. But despite its rarity, MCC is one of the most aggressive skin cancers, with a cancer-specific mortality rate more than twice that of melanoma.
How MCC Compares to Other Skin Cancers
To put the numbers in perspective: between 2000 and 2021, cancer registries captured 19,444 cases of MCC compared to 646,619 melanomas. Basal cell and squamous cell carcinomas, the two most common skin cancers, collectively account for millions of diagnoses each year. MCC sits at the far end of the rarity spectrum for skin cancers.
What makes MCC notable despite those small numbers is how dangerous it is. A comparative study spanning two decades found that patients with MCC had 2.3 times the cancer-specific mortality of melanoma patients. Five-year overall survival is roughly 51% when the cancer is still localized, drops to 35% when it has reached nearby lymph nodes, and falls to 14% once it has spread to distant organs.
Cases Are Rising, Not Falling
MCC is rare, but it’s becoming less so. Between 2000 and 2013, the number of reported cases in the U.S. nearly doubled, a 95% increase that outpaced even melanoma’s 57% rise over the same period. While the overall rate of solid tumors actually declined during those years, the most aggressive skin cancers moved in the opposite direction.
The main driver is demographics. MCC risk climbs sharply with age, and as the baby boom generation moves into higher-risk age brackets, case counts are projected to keep climbing. Researchers estimated roughly 2,500 annual U.S. cases around 2013 and projected that number would exceed 3,250 by 2025. The American Cancer Society’s current estimate of about 3,000 cases per year tracks closely with those projections.
Who Gets MCC
The typical MCC patient is an older white male. The median age at diagnosis is 73, and 90% of patients are over 50. Men account for roughly two-thirds of cases, consistent with the pattern seen across most skin cancers and likely related to cumulative sun exposure.
People with weakened immune systems face dramatically higher risk. Organ transplant recipients, who take medications that suppress the immune system to prevent rejection, develop MCC at 24 times the rate of the general population (12.8 cases per 100,000 person-years versus about 0.7). People living with HIV, those with certain blood cancers, and anyone on long-term immune-suppressing therapy also carry elevated risk.
Two Pathways to the Same Cancer
MCC has an unusual biology. About 80% of tumors contain genetic material from a common virus called Merkel cell polyomavirus. Most people are exposed to this virus at some point in life without consequences, but in rare cases, the viral DNA integrates into a skin cell’s genome and drives uncontrolled growth. The remaining 20% of MCC cases are virus-negative and instead driven by extensive DNA damage from ultraviolet radiation, similar to other skin cancers.
These two pathways have slightly different profiles. UV-driven tumors tend to carry a much heavier load of genetic mutations and are relatively more common in men. Virus-positive tumors are more frequent in women and in people whose immune systems are compromised, since a healthy immune system normally keeps the virus in check.
What MCC Looks Like
One reason MCC is often caught late is that it doesn’t look particularly alarming at first. It typically appears as a firm, painless, dome-shaped bump on the skin, often flesh-colored, red, or bluish-purple. Dermatologists use the acronym AEIOU to describe the most common features at diagnosis:
- Asymptomatic: 88% of patients report no pain or tenderness
- Expanding rapidly: 63% of tumors grew noticeably within three months
- Immunosuppressed: a meaningful minority of patients have weakened immune systems
- Older than 50: 90% of patients
- UV-exposed site: 81% of tumors appear on sun-exposed skin, particularly the head and neck
Because the bump is painless and can resemble a cyst or other benign growth, many people and even some clinicians don’t suspect cancer right away. A rapidly growing, painless nodule on sun-exposed skin in someone over 50 should prompt a biopsy.
Recurrence After Treatment
Even after successful initial treatment, MCC recurs at high rates. In a large study of 618 patients tracked at a major cancer center, 223 (about 36%) experienced a recurrence. How likely that is depends heavily on stage. Patients with early-stage, localized disease (stage I) had roughly an 80% chance of remaining free of recurrence and alive at five years. For stage IIIB disease, that number dropped to about 40%, and for stage IV it fell below 35%.
Most recurrences happen within the first two to three years. After that window, the risk drops considerably, though ongoing monitoring remains important. The median follow-up in the study was just over three years for all patients and 4.3 years for those still alive at their last check-in, which gives a reasonable picture of the critical early period after diagnosis.
Why Rarity Matters
The rarity of MCC has real consequences for patients. Because most physicians rarely see it, the cancer is frequently misdiagnosed initially, sometimes as a benign cyst, insect bite, or other harmless skin lesion. Delays in diagnosis allow the tumor to advance, and MCC spreads quickly compared to other skin cancers. A tumor that might have been curable as a small localized nodule can become far more dangerous once it reaches the lymph nodes.
Rarity also means that large clinical trials are harder to run, so treatment advances have historically lagged behind those for melanoma. That said, immunotherapy drugs introduced in recent years have improved outcomes for advanced MCC, and cancer-specific mortality has shown improvement for both MCC and melanoma patients since around 2011. For a cancer this aggressive, catching it early remains the single most important factor in survival.