WHERE DO WE STAND AND IS THERE ANY GOOD NEWS?
It has to be admitted that on a quick glance there doesn’t seem to be much to be cheerful about. The predictions for the worldwide increase in cancer rates are almost beyond comprehension and, as we’ve noted in passing, there isn’t anywhere to hide. Certainly not in the UK where in 2008 there were 309,527 new cancer cases, an increase of 54,000 compared with 1994. In particular, there was a 15% increase in breast cancer and sharp increases in bowel and prostate cancer. Of course, part of the reason for the increasing trends is that we are living longer and, as we saw earlier, cancers are mainly diseases of old age. Even so, cancers also afflict the young. The ~156,000 cancer deaths/year makes up ~25% of all UK deaths but that proportion rises to 36% for all deaths under the age of 65 and it’s ~50% for deaths in women under 65. This reflects sub-sets of cancer (e.g. childhood cancers and aggressive forms of breast cancer, as we noted earlier) that are relatively rare but have a big statistical impact on an age group that, by and large, don’t tend to die from other causes.
Some encouragement may be had from the progressively earlier detection of the disease through improved screening programmes (Fig. 1) together with the development of effective drug treatments.
1.Imaging breast tumours.
This has been particularly true for cervical and breast cancers and has meant that the developed world has seen a steady improvement in the five-year survival rate for breast cancer. Overall in the richest countries, about 50% of cancer patients survive the disease. However, in the developed world you are more than twice as likely to be diagnosed with cancer than elsewhere, with the result that in developing countries 80% of initial diagnoses are of late-stage, incurable tumours.
Thus generally the world needs to improve the screening programmes referred to earlier, but we could also do much more by way of prevention. In developed countries, only about 8% of cancers arise from infections but elsewhere almost one quarter are caused by agents such as HBV and HCV (liver cancer), HPV (cervical and anogenital cancers) and bacteria. Thus, for example, 80% of deaths from cervical cancer are in developing countries. We noted the efficacy of HBV and HPV vaccines and it is to be hoped that these will become sufficiently available to make a major impact on the incidence of the cancers promoted by these viruses. Despite these wonderful contributions by science, it is difficult to be optimistic about controlling cancer in Africa, given the economic and logistical problems. The setting up in 2008 of AfrOx to bring UK expertise to bear on the African cancer problem is at least one encouraging step.
In the UK the picture is somewhat mixed. Better diagnosis and treatment has produced an annual decline in cancer deaths since 1983. The long-term survival rate is ~40% although the figure varies widely across the ~200 distinct forms of cancer (Fig. 1.13). Of these, as we noted earlier, four types (breast, bowel, prostate and lung) account for ~50% of adult cancer deaths in the UK. In the period from 1984 to 2004 the five-year percentage survival rates for the first three of these cancers improved, prostate from 42 to 74%, breast from 59 to 81% and bowel from 40 to 50%. For lung cancer, the rate remained unchanged at 5%. The most dramatic improvements of all have been for testicular cancer and some childhood cancers where the five-year survival rate has gone from being very low 20 years ago to >90%. These large differences in the survival rates and in the impact that medical research is having arisen from the fact that although, as we shall see, there are some basic features that apply to most if not all cancers, distinct molecular mechanisms drive the diseases and they arise in different types of cell. For these reasons, no single therapeutic regime is likely to be fully effective even against one cancer type yet alone against all. The one advantage of this diversity from the point of view of devising therapeutic strategies is that cancers present many potential targets for slowing or reversing their progress.