Cancer Trends
In 2006, there were 24 488 incident cases of cancer in Norway, of which 12 903 occurred among men and 11 585 among women (Table 4). The four most common forms continue to be cancers of the prostate, female breast, colon and lung, and they are responsible for half of the total cancer burden (12 277 new cases). Prostate cancer is the most frequent cancer in men (3815), followed by colorectal (1686) and lung cancer (1369). With 2673 new cases in 2006, breast cancer is the most frequently-occuring neoplasm in women, colorectal and lung cancer rank second and third, with 1767 and 953 incident cases, respectively.
Cancer rates increase rapidly with age, and the vast majority in Norway – about 85% in men and 75% in women occur in persons aged over 55 (Figure 3). The highest proportion of cancers occur in the 55-74 age group, with close to half of all cancers diagnosed in men, and approximately 40% of those diagnosed in women, occurring within this age range. A further one-third of the burden cancer affects elderly men and women (aged 75 or over). It is of note that close to one in five cancers diagnosed in women occur within the ages 30 to 54, a higher proportion than seen in men (about one in ten men).
The relative impact of different forms of cancer varies considerably with age. Figure 4 identifies those cancer sites that contribute substantially to the disease burden in children (aged 0-14), adolescents and young adults (15-29), the middle-aged and the elderly (30-54, 55-74 and age 75 or over).
Table 3 compares the age-standardised rates and sex ratios for selected cancer types in 1978-1982 and 2002-2006. Men tend to have an excess of incidence for most cancer forms in both time periods, with the exceptions of melanoma of the skin, and, most notably, thyroid cancer. The highest male:female (M:F) ratios are seen for several head and neck cancers, although a number of the most frequent cancer forms - lung, bladder, stomach and rectum - are consistently more common among men. The declines in M:F ratios for several neoplasms over the 25 year period may be explained by decreasing trends among men, increasing trends among women, or indeed a combination of both. For lung cancer, the halving of the M:F ratios during the last quarter century points to a more rapid increase in trends in female rates relative to those in men.
The time trends of selected cancers in Figure 5 provide more detail regarding the changing evolution of cancer risk among Norwegian men and women. Of note are: 1) the unparalleled rise in prostate cancer incidence since 1990, largely as a result of the rapidly increasing use of the Prostate Specific Antigen (PSA) test since it became commercially available in 1989; 2) the continued increases in both breast cancer and lung cancer among women, and colon cancer in both sexes; 3) the continuing declines in stomach cancer in both sexes; and 4) the rapid increases in a number of cancers for which the underlying causes (and prospects for primary prevention) remain enigmatic: testicular cancer in men and non-Hodgkin lymphoma in both sexes.
The total burden of cancer in Norway - expressed as the number of new cases - has been increasing in the last decade (Table 4 and 5), as it has been since the Registry began reporting. This observation reflects real increases in the risk of several common cancers including female breast, colorectal and lung cancer, but it also relates to an increasing ability to diagnose the disease with time, particularly for prostate cancer in the 1990s. The increases in these common cancers are partially compensated by decreasing incidence trends of several cancer types, notably stomach cancer (in both sexes) and cervix cancer in women. Melanoma of the skin is stabilising in both sexes, while rates of lung cancer in men are beginning to decline (Figure 5).
As was described in Figure 1, a larger proportion of the increasing burden can be attributed to the demographic effects of population growth and ageing (see the special issue of CiN 2005, for predictions of cancer in Norway up to 2020, by Health Region.)
Tables 6-19 provide further information on the distribution of cancer incidence in Norway. The number of incident cases and rates are tabulated according to year of diagnosis, age group and county of residence.