Incidence the rate at which new cases are diagnosed is an important statistic as well. If different countries have different incidence rates, most observers conclude that we now have real differences in the underlying frequency of the cancer, which may help us find out more about why people get cancer. And if incidence is rising in a country, many will also conclude that morbidity (harmful effects other than death) and mortality from cancer are destined to increase. Occasionally someone will even use a frightening term: cancer epidemic.
Let's return to kidney cancer and consider what is happening to its in cidence. It's rising: the age-adjusted rate is more than double what it was 50 years ago. Is there an epidemic of kidney cancer? In a word: no. I don't know anyone who believes that all of the rising incidence is real that is, that people are truly developing kidney cancer at twice the rate of 1950. Instead most, if not completely, of the increased incidence is caused by doctors finding kidney cancer more often.
In a perfect world, testing for cancer wouldn't influence how many patients are diagnosed, it would only influence when they're diagnosed. In reality, however, testing can dramatically influence the cancer incidence rate (see appendix at the end of this article).
This phenomenon undoubtedly explains the increased incidence observed in cancers of organs deep inside the body. These organs are in places we couldn't see using conventional X-rays. Then came ultrasounds, CAT scans, MRIs, and the ability to direct skinny needles into these organs to perform biopsies. As a result since 1950 numerous "epidemics" have seemed to appear. The incidence of cancers of the brain is up 70%, kidney cancer up 130%, liver cancer up 180%, and prostate cancer up 195% almost three times the incidence in 1950. The word epidemic has been most frequently used to describe the cancer incidence for a more accessible organ: the breast. The main 65% increase in breast cancer incidence is also caused by testing more women undergoing ever more sensitive mammograms.
Oddly enough, the effect of testing on incidence is most dramatic for a cancer in an organ that sees the light of day: the skin. The cancer is melanoma, and it arises from the skin cells that produce pigment. Its incidence is up 477%, almost six times what it was in 1950. Most of the increase has been in early-stage cancers, ones less than 1. mm thick.
While some of this increase could be the result of increased exposure to the sun, most of it is probably related to increased exposure to dermatologists. Their cancer test is a skin biopsy. In the past, a skin biopsy involved minor surgery. The skin was cleansed, covered with drapes, and injected with an anesthetic; then the doctor would use a scalpel to carefully cut away an ellipse of skin (a shape having a better cosmetic result).
The hole would be closed with some stitches, and the patient would come back a few days later to have them removed. Now a skin biopsy is typically done with a punch a tool roughly the size of a pencil with a circular blade on the end. The punch takes a little circle of skin about this big: hole. The hole gets one stitch or is sometimes just covered with a Band-Aid. Less pain, less work, less tissue, less time and that equals more biopsies. Furthermore, all doctors have been sensitized to consider melanoma. As a medical student, I remember a campaign to have us look thoroughly at all the skin of all patients.
We were given little pocket cards reminding us what to consider. Patients with any suspicious moles were to be sent to dermatologists. That is how we screen for skin cancer, and it's been going on in doctors' offices for years. But it's getting more common. And you will imagine the chain of events: more people are referred to dermatologists, 18 more people get biopsied, more people are diagnosed with melanoma and the incidence rate goes up.
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