12.1: Trends in Cancer Rates

Be wary of how statistics are presented. Cancer rates must be age-adjusted when comparing one time period with another, just as prices are adjusted for inflation. Ideally, we’d also adjust for changes in socioeconomic status, ethnic make-up, etc., but this is hard to do.

The age-adjusted overall cancer death rate had been rising because of lung cancer (Figure 1.4). Excluding lung cancer, however, this rate has fallen over the last 90 years. In 1930, the leading cause of death from cancer was cancer of the stomach for men, and of the uterus for women (Table 12-1). Now it’s lung cancer for both men and women (Table 12-2).

Table 12-1: Cancer Death Rates, U.S., 1930-2019

What about occurrence rates? Are they going up? This is a harder question. Whereas all deaths are recorded, we don’t have a national office that records every occurrence of cancer.

Occurrence rates are estimates based on sample populations. Most of the data only go back to 1973, when the National Cancer Institute began the Surveillance, Epidemiology, and End Result program (SEER.cancer.gov) to gather data from selected areas of the country. These limited data are the main source of information on occurrence rates, survival times, etc.

The rates are based on the number of new cases diagnosed and reported in the sample population. If you get cancer in 2020 but it isn’t diagnosed until 2022, it’s counted as occurring in 2022, since only the diagnosis date can be pinpointed.

If it isn’t diagnosed or reported, it isn’t counted at all. Thus, there can seem to be changes in occurrence when, in fact, the changes are related to diagnosis, e.g., when former First Lady Betty Ford got breast cancer, women became more aware of it, more women got checked, and more were diagnosed that year.

Likewise, when screening is promoted or when new tests detect cancer earlier, the rate will seem to rise, and cancer will seem to be occurring at a younger age.

Brain tumors can be diagnosed by imaging methods, raising both its reported occurrence and its listing as a cause of death. In the past, some brain tumors could only be diagnosed by going into the brain. If you died of an undiagnosed brain tumor and an autopsy wasn’t done, the cause was often listed as a stroke (the more likely cause of death involving the brain).

If a man is cured of colon cancer at age 60 and gets prostate cancer at age 80, two occurrences of cancer are counted for the one person. In contrast, death—as the saying goes—is one to a customer.

Whereas all deaths from cancer are included in cancer death rates, some highly curable cancers are excluded from some occurrence rates. For example, more non-melanoma skin cancer is diagnosed in the U.S. than the combined total of lung, colon, breast, and prostate cancer, but it usually doesn’t spread and is easy to remove.

In contrast, melanoma skin cancer (from pigmented cells, e.g., mole) spreads fast. There’s much less time to find and remove it. The 5-year survival is 99% if it hasn’t spread, 68% if it has spread regionally, but only 30% if it has spread further. Thus, when occurrence rates of skin cancer are compared, the focus is on melanoma.*

The dramatic rise in prostate cancer diagnoses in the late 1980s (Figure 12.1) doesn’t necessarily mean that there’s been such a rise in its actual occurrence. Diagnosis rates are based on the number of people in the population, not on the number examined.

More diligent reporting, more sensitive tests, and more insurance companies paying for routine screening can also raise diagnosis rates. To get a best estimate of changes in occurrence rates, the entire population would have to be screened every year by the same method.

When breast self-exams and mammograms are promoted with increasing success, the diagnosis rate goes up, regardless of whether actual occurrence goes up. Similarly, the diagnosis of prostate cancer went up dramatically with the promotion of screening via prostate-specific antigen (PSA) blood tests and digital rectal exams (finger in rectum to feel the prostate gland).

When new screening tests become available, those in higher socioeconomic groups usually get tested first and in greater numbers, e.g., women with more education get more mammograms. This can distort diagnosis rates.

^{*2022 estimates of skin melanoma in U.S.: 99,780 cases, 7,650 deaths. Melanoma had been rising for decades in young, fair-skinned adults. It seemed for awhile to stop rising, but this was because insurance began providing more coverage when it was treated outside a hospital—more cases treated this way and fewer reports of melanoma. When this underreporting was corrected, the occurrence rate continued upward.}