Trends in colorectal cancer mortality in Japan, 1970–2000

A comparative study of trends in colorectal cancer incidence in the Miyagi Prefecture of Japan and Connecticut, USA, from 1959 to 1992 showed substantial rises for both colon and rectal cancer in Japan. For Japanese men born around 1930, values were comparable to—or even higher than—those of Connecticut white men.1 Colorectal cancer incidence, however, is not only due to changes in underlying rates of the disease, but is also influenced by advancements in screening and early diagnosis.2, 3, 4 National mortality rates are less influenced by any such modification and provide therefore less biased information on long-term trends. In a previous study, we considered trends in mortality from colorectal cancer in Japan from 1955 to 1989.5 Overall age-standardized rates increased from 7.0 to 14.6/100,000 in men and from 6.0 to 9.5/100,000 in women. However, a tendency toward a leveling off and a subsequent decline of rates in the younger age groups were observed since the early 1980s.5, 6 From these age-specific trends, we inferred therefore that—in the absence of major differences in aetiologic and biologic correlates of colorectal cancer at young and elderly ages—colorectal cancer mortality in Japan was unlikely to further increase.6 A recent analysis on colon cancer incidence and mortality in Japan from 1950 to 2000 in relation to dietary habits reported increasing trends up to the early 1990s, with a subsequent leveling off thereafter, probably reflecting the changes in dietary factors, including meat consumption, as well as other lifestyle factors in the Japanese population.7 To provide updated information on this issue, we have therefore considered trends in colorectal cancer mortality in Japan over the last 3 decades, using data from the World Health Organization (WHO). Official death certification data for colorectal cancer were abstracted from the WHO database over the period 1970–2000.8 During the calendar period considered, 4 different revisions of the International Classification of Diseases (ICD) were used.9, 10, 11, 12 Thus, classifications of cancer deaths were recoded, for all calendar periods, according to the Ninth Revision of the ICD.11 To improve validity and comparability of data throughout different calendar periods, we considered all intestinal sites combined (ICD IX 152–154 and 159.0). Estimates of the resident population, based on official censuses, were obtained from the same WHO database.8 From the matrices of certified deaths and resident populations, age-specific rates for each 5-year age group and calendar periods were computed. Age-standardized death rates per 100,000 at all ages, truncated 35–64 years and for 3 different age groups (25–44, 45–64, ≥65 years), were computed using the direct method and based on the world standard population13 in order to allow comparison with mortality rates from North America and other countries of the world. The joinpoint regression model was used to describe changes in trends over successive periods of time. This type of nonlinear regression model allows the identification of the best fitting point(s)—called “joinpoint(s)”—where the rates significantly change.14 The estimated annual percent change (EAPC) was then calculated for each of the identified trends by fitting a regression line to the natural logarithm of the rates using calendar year as a regressor variable (i.e., given y=a + bx, where y = ln(rate) and x = calendar year, the EAPC is estimated as 100*(eb−1)). The joinpoint analysis was performed using the Joinpoint software from the Surveillance Research Programme of the U.S. National Cancer Institute.15 Figure 1 shows the trends in age-standardized death rates for cancer of the intestines (mainly colon and rectum) in men and women at all ages and truncated 35–64 years (Fig. 1a) and in 3 different age groups (Fig. 1b–d) across subsequent quinquennia between 1970 and 1999 and year 2000. Overall mortality rates from colorectal cancer increased in Japanese men from 10.20/100,000 in 1970–74 to 17.32/100,000 in 1995–99 but leveled off to 16.32/100,000 in 2000. Death rates in women increased from 8.00/100,000 in 1970–74 to 9.95/100,000 in 1990–94 and stabilized thereafter (9.74/100,000 in 2000). Truncated rates in men aged 35–64 years showed an upward trend up to the mid 1990s (from 13.24/100,000 in 1970–74 to 21.29/100,000 in 1990–94), then leveled off in the late 1990s and declined to a value of 20.67/100,000 in 2000. Similarly, truncated death rates in women increased from 10.93/100,000 in 1970–74 to 13.84/100,000 in 1990–94 and showed a tendency to stabilize or decrease thereafter (12.69/100,000 in 2000). In the younger age group (25–44 years), mortality from colorectal cancer was about 2–3/100,000 in men and 1–2/100,000 in women and tended to decline since the early 1980s in both sexes (Fig. 1a). At age 45–64 years, colorectal cancer mortality started to level off in the early 1990s and to decline since the mid 1990s. At age 65 or more, rates leveled off only since the late 1990s for men, while rates in women have been moderately upward over the last 2 decades. Trends in age-standardized (world population) mortality rates per 100,000 men and women from colorectal cancer, overall and in various age groups, Japan, 1970–2000. (a) All ages and truncated at age 35–64 years; (b) 25–44 years; (c) 45–64 years; (d) ≥65 years. Solid line with crosses, men; solid line with squares, women; dashed line with crosses, men, truncated (35–64 years); dashed line with squares, women, truncated (35–64 years). A further investigation of trends in colorectal cancer mortality for the period 1970–2000 using the joinpoint analysis (Table I) indicated that overall rates significantly increased up to 1996 (with a peak of 17.53/100,000) in men and up to 1992 (with a peak of 10.09/100,000) in women and then declined. Truncated rates in men tended to level off from 1990 to 1996 and showed a downward trend thereafter; in women they started to decline in 1992. Earlier trends were observed in the younger age group, with a significant downward trend since the early 1970s in men and since 1975 in women. This updated analysis of trends in mortality from colorectal cancer in Japan indicates that after a steady rise of rates up to the middle 1990s, death rates tended to level off in the last years in both sexes. The favorable trends in the younger age group, where declining rates were observed since the early 1970s, and the reversal of trends in middle-aged adults since the early 1990s confirm the presence of cohort effects, which are likely to continue in the near future, suggesting a likely further decrease in colorectal cancer mortality in Japan.16 The rapid increase in colorectal mortality in Japan over the past decades has generally been attributed to the introduction of a “western” diet typical of North America and Western Europe, characterized by a high intake of animal fats and meat (particularly red meat) and a low consumption of cereals and fibers.17 Other lifestyle changes related to the economic development and westernization of Japan, such as a decrease in energy expenditure and a consequent increase in body mass index, could also have played a role in earlier unfavorable trends in colorectal cancer.18 The reasons for the decline in colorectal cancer mortality observed over recent years in Japan, as well as in the USA5 and several European countries,19 are complex and not completely understood. The observed trends, particularly in the young Japanese generations, likely reflect favorable modifications in (dietary) risk factors exposure, including a stabilization in the consumption of fats and meat and a wider availability of vegetables.7, 20 An early diagnosis3, 4, 21 and an improved treatment of the disease22 could also have had an effect on the decline in colorectal mortality, although their role in colorectal cancer mortality remains open to debate.23 Diagnosis and certification of cancer of all intestinal sites, including colon and rectum, have long been sufficiently reliable and have not substantially changed in the last 3 decades, thus permitting meaningful inference of trends. Although the distinction between colon and rectum may pose some problems, since a large proportion of cancers arise in the recto-sigmoid junction,13, 24 this should not have affected our estimates based on all intestinal cancers combined. Thus, it is unlikely that changes in diagnostic and certification practices for colorectal cancer can explain the recent decline in mortality trends in Japan. Although recent colorectal mortality rates are higher in Japan than in the USA—where a decline started about 15–20 years before5—they are still considerably lower than in several countries from central and northern Europe.19 Furthermore, the recent reversal of trends in colorectal cancer mortality, particularly in young generations, suggests that they are likely to further decrease in the near future. Yours sincerely, The authors thank Mrs. M.P. Bonifacino for editorial assistance. Cristina Bosetti, Matteo Malvezzi, Liliane Chatenoud, Eva Negri, Fabio Levi, Carlo La Vecchia.