Appendix cancer is one of the rarest cancers in the body, affecting fewer than 2 people per 100,000 each year in the United States. To put that in perspective, colorectal cancer is roughly 40 times more common. But while appendix cancer remains rare, it’s becoming significantly less so: incidence has jumped by 232% over the past two decades, and the reasons aren’t fully understood.
How Common Is It by the Numbers
Between 2000 and 2017, the overall incidence of appendiceal tumors was 0.93 per 100,000 people per year, based on data from the SEER database covering about 30% of the U.S. population. By the end of that period, the rate had climbed to 1.72 per 100,000. During those 18 years, roughly 13,500 cases were identified in the database alone.
Deaths from appendix cancer have also risen. The age-adjusted mortality rate tripled from 0.08 per 100,000 in 1999 to 0.24 in 2017, then leveled off through 2023. Over that full 25-year span, nearly 16,000 Americans died from the disease.
Most Cases Are Found by Accident
Appendix cancer rarely announces itself with obvious symptoms. The vast majority of cases are discovered incidentally, typically when a surgeon removes an inflamed appendix and a pathologist examines the tissue afterward. Fewer than 2% of all appendectomies reveal a tumor, though one study found the rate was closer to 2.8% when patients came in with what looked like straightforward appendicitis. Part of the recent increase in diagnoses likely reflects more thorough examination of removed appendix tissue, not just a true rise in disease.
Types of Appendix Cancer
There are two broad categories. Neuroendocrine tumors (sometimes called carcinoid tumors) grow from hormone-producing cells in the appendix wall and are the most common type. These drove most of the incidence increase over the past two decades, rising from 0.03 to 0.90 per 100,000 per year. They tend to be slow-growing and often have a favorable outlook when caught early.
Epithelial cancers, also called adenocarcinomas, grow from the lining of the appendix. Within this group, mucinous neoplasms are a particularly complex subtype. These tumors produce a gel-like substance called mucin. If the appendix ruptures or the tumor leaks, that mucin can spread throughout the abdominal cavity, leading to a condition called pseudomyxoma peritonei (PMP). Nearly all PMP cases originate from the appendix, even when the disease is first noticed in other organs like the ovaries.
Who Gets It
One of the most striking features of appendix cancer is how often it strikes younger people. About one in three patients is under 50 at diagnosis, a far higher proportion than colorectal cancer, where only about one in 10 patients is that young.
Race and ethnicity also matter. Five-year survival rates differ meaningfully: 75.5% for non-Hispanic White patients and 75.4% for Hispanic patients, but 63% for non-Hispanic Black patients. Black patients are more likely to be diagnosed with non-mucinous adenocarcinomas, which tend to be more aggressive. Among younger patients with adenocarcinoma specifically, men have significantly lower survival rates than women.
Survival Rates by Stage
Prognosis varies enormously depending on how far the cancer has spread at diagnosis and what type it is. For non-mucinous cancers, five-year survival rates for early-stage disease are encouraging: around 90% for stage I and 88% for stage IIA. Even some stage III cancers have relatively high survival, with stage IIIA at 82% and IIIB at 64%.
The picture changes dramatically once the cancer spreads to distant sites. Stage IVA survival drops to about 35%, stage IVB to 24%, and stage IVC to just 14%. Because appendix cancer often doesn’t cause symptoms until it has spread within the abdomen, a meaningful number of patients are diagnosed at later stages.
Treatment for Advanced Disease
For tumors confined to the appendix, surgery to remove the appendix (and sometimes part of the colon) is often the only treatment needed. The challenge comes with mucinous tumors that have spread throughout the abdominal cavity.
The standard approach for peritoneal spread combines two procedures done in a single operation: surgeons first remove as much visible tumor as possible from the abdominal surfaces, then bathe the abdominal cavity in heated chemotherapy to kill microscopic cancer cells left behind. This combined approach can produce long-term survival even in advanced cases. In a randomized trial with 10-year follow-up, median survival exceeded 5.6 years in one treatment group and reached 9.1 years in another, depending on the chemotherapy agent used. For patients with high-grade tumors, outcomes were less favorable, with median survival ranging from roughly 2 to 3.5 years.
No standardized chemotherapy regimen exists for advanced appendix cancer. Unlike colorectal cancer, which it superficially resembles, appendix cancer has distinct molecular features and doesn’t respond to the same drugs. This is an ongoing challenge given how rare the disease is, since it’s difficult to run large clinical trials.
Why the Increase
The 232% rise in incidence over two decades is likely a combination of factors. More appendectomies are being performed (partly due to better imaging that catches borderline cases of appendicitis), pathologists are examining specimens more carefully, and classification standards have evolved to capture tumors that might previously have been overlooked or categorized differently. Whether there is also a true biological increase in the rate of these tumors remains an open question, but the trend is consistent enough that researchers at institutions like Vanderbilt University Medical Center have flagged it as a growing public health concern, particularly among younger adults.