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Rare cancers represent 20% of US cancer diagnoses
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Rare malignancies accounted for about one in five cancer diagnoses in the United States from 2009 to 2013, according to an American Cancer Society report published in CA: A Cancer Journal for Clinicians.
Further, more than two in three cancers diagnosed in children and adolescents are considered rare, and that proportion is likely to grow as the use of molecular markers increases, results showed.
“There is a dearth of information on rare cancers in the United States,” Carol E. DeSantis, MPH, director of breast and gynecological cancer surveillance at the American Cancer Society, told HemOnc Today. “In the last several years, researchers in Europe and Japan published reports on rare cancers in those areas. We undertook this study to provide a comprehensive review of rare cancer statistics and to highlight the burden of rare cancers in the United States.”
Researchers used data from the North American Association of Central Cancer Registries and the SEER program to comprehensively examine contemporary incidence rates, stage at diagnosis, and survival for 181 rare cancers — defined as incidence fewer than six cases per 100,000 individuals per year — from 2009 through 2013.
Researchers categorized 119 of the rare cancers — 3% of all cancer diagnoses — as very rare due to an incidence rate at or below 0.05 per 100,000. Ten percent of cases (n = 775,645 of 7,465,548) could not be classified as rare or common cancers.
Rare cancer diagnoses occurred slightly more frequently among males than females (21% vs. 19%), as well as in Hispanics (24%) and Asian/Pacific Islanders (22%) than black (20%) and white (19%) individuals.
Rare cancers represented a greater proportion of cancers diagnosed in patients aged younger than 20 years (71%) than those aged 20 years to 39 years (39%) and 40 years or older (17%-20%). Rare diagnoses most often occurred as hematopoietic (38%) and digestive system (36%) cancers, which include cancers that occur in the oral cavity and pharynx. Rare cancers also comprised nearly one-third (31%) of cancers of the female genital system.
When researchers evaluated specific rare cancers by race/ethnicity, they observed that some cancers that are rare overall are more common in certain groups. For instance, white patients showed the highest rates and black patients showed the lowest rates of transitional cell carcinoma of the pelvis (2.06 vs. 0.85 per 100,000) and ureter (1.07 vs. 0.52 per 100,000).
Further, malignant thymoma is a very rare cancer (< 0.5 per 100,000), but rates are twice as high in black and Asian/Pacific Islander men and women than white men and women.
Patients with rare cancers showed worse 5-year relative survival than for common cancers in males (55% vs. 75%) and females (60% vs. 74%). Substantially more patients diagnosed with a rare cancer at age 39 years or younger achieved 5-year OS than those aged older than 39 years (80% vs. 60%).
From a clinical perspective, rare cancers are challenging to diagnose and treat and present a number of unique challenges, from difficulties and delays in diagnosis to finding oncologists who specialize in those cancers, DeSantis said.
“There has been little progress in detecting rare cancers, with few exceptions such as rare breast cancer subtypes that can be detected by mammography, along with more common types of breast cancer,” DeSantis said. “Although there has been progress for the treatment of some specific rare cancers — [for example, gastrointestinal stromal tumors and many childhood cancers] — in general, progress has been limited. Some of the inherent challenges include limited research funding and difficulty in accruing sufficient patients to study in clinical trials. As a result, patients with rare cancers as a group are more likely to be diagnosed at late stage and have poorer survival.”
Solid tumor diagnosis occurred at regional or distant stages in 59% of rare cancers compared with 45% of common cancers.
It is important to note that there is no universally accepted definition for rare cancers, DeSantis said.
“More and more patients will be diagnosed with a rare cancer as knowledge of the molecular biology of cancers increases and more common cancers are subdivided into a collection of subtypes,” DeSantis said. – by Chuck Gormley
For more information:
Carol E. DeSantis, MPH, can be reached at Surveillance and Health Services Research, American Cancer Society, 250 Williams St. NW, Atlanta, GA 30303; email: carol.desantis@cancer.org.
Disclosure: The researchers report no relevant financial disclosures.
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