Preventing cancer

Cancer is largely avoidable.

Epidemiological evidence points to a strong correlation between diet and certain diseases such as cancer and cardiovascular disease.

Will the 1990s be remembered as "the decade when we measurably turned the tide against cancer"? The US study, Annual Report to the Nation on the Status of Cancer, 1973-1998 reports an annual decline of 1% per annum. Many find this conclusion misleading. Taking several factors into account, it is not clear that there has been any decrease at all. First, lung cancer, which is in no way due to medical advances, accounts for the lion's share of the cancer rate decline. Take lung cancer out of the equation, and the reported decline in cancer is cut by a third. Second, it overlooks the fact that overall cancer rates rose by more than a factor of ten during the 20th century and increasing over 20% just from 1973 to 1992. The incidences of ten other cancers have increased from 1992 to 1998. These include cancer of the liver, thyroid, oesophagus, small intestine and heart, plus non-Hodgkin's lymphoma, melanoma and breast cancer. Thirdly, certain cancer types are not counted, notably in situ carcinomas, which are an early stage of cancer in which the tumour is confined to the organ where it first developed. For example, breast cancer rates have increased 40% from 1975 to 1998. Not included in the statistics are incidences of two types of in situ breast cancer, one that develops in the milk passages (ductal carcinoma in situ (DCIS)) and another than develops in the milk-producing glands (lobula carcinoma in situ (LCIS). Because these tumours have not invaded neighbouring tissue, the standard treatment of surgery (lumpectomy or full mastectomy), radiation and chemotherapy is usually effective in stopping its spread. The incidence of in situ breast cancers has surged and continues to increase: The American Cancer Society estimates that 46,400 American women will have been diagnosed with DCIS or LCIS in 2001. Adding these in situ cancers to invasive breast cancers would increase the incidence rate by 24%.

Neither does the survey count in situ melanoma skin cancers, with which the American Cancer Society estimates 31,400 Americans will be diagnosed in 2001. Adding these cases would increase the rate for skin cancer by 56%.

Changes in diagnostic procedures also affect incidence rates. In explaining fluctuations in the incidence of prostate cancer, for example, the National Institutes of Health noted that with the advent of Prostate Specific Antigen (PSA) screening in the late 1980s, there was a spike in the incidence of prostate cancer, not because more men were suddenly getting the disease above the normal increase, but because previously undetected cancers were suddenly being diagnosed. Now that the prevalent cancers have been detected, what looks like a decline in incidence in the 1990s, they say, is not due to fewer men getting prostate cancer, but is a decline relative only to the abnormally high number of tests and diagnoses made just previous to that period.