In the United States the median age at which colon cancer strikes is 69 for men and 73 for women. In Chad the average life expectancy at birth is about 50. Children who survive childbirth — and then malnutrition and diarrhea — are likely to die of pneumonia, tuberculosis, influenza, malaria, AIDS or even traffic accidents long before their cells accumulate the mutations that cause colon cancer.  In fact, cancers of any kind don’t make the top 15 causes of death in Chad — or in Somalia, the Central African Republic and other places where the average life span peaks in the low to mid-50s. Many people do die from cancer, and their numbers are multiplied by rapidly growing populations and a lack of medical care. But first come all those other threats.  How different this is from the United States, where oncologists are working to rid a 91-year-old former president of metastatic melanoma, one of the deadliest cancers. One of Jimmy Carter’s drugs, a new immunotherapy agent called Keytruda, has been priced at $12,500 a month, in addition to the cost of his surgery and treatment with computer-guided radiation beams.  Mr. Carter, a religious man, says he is prepared to meet his maker. But he is among the fortunate who first have the luxury of exhausting the most expensive remedies medicine has to offer.  So far the approach appears to be working, shrinking his brain tumors to invisibility. Should there be a setback, his doctors may have the option of combining Keytruda with other recently approved immune system therapies, the next line of defense. Last summer at the annual meeting of the American Society of Clinical Oncology, Dr. Leonard Saltz, chief of gastrointestinal oncology at Memorial Sloan Kettering Cancer Center, estimated that medical bills for these cocktails could run $300,000 a year.  That is for just one person. For those with the will and the resources, the war on cancer has come to mean pushing incrementally toward some imagined immortality, the ultimate right to life. There appears to be no limit to what we — society in the abstract — will agree to pay for extending long and well-lived lives.  Vice President Joseph R. Biden Jr. was envisioning more of these death-defying acts when, borrowing a metaphor, he recently called for a “moon shot” to end cancer — infusions of additional dollars that, judging from the past, would go largely toward research that helps older people become older.  Children with leukemia, lymphoma or osteosarcoma might also benefit, along with some younger adults and those just reaching their prime, like the vice president’s son, Beau Biden, who died this year from a brain tumor at age 46. But the median age of diagnosis for cancers of all kinds in this country is 66. Seventy-eight percent of cases are diagnosed in people 55 or older. Childhood cancer, among the most curable, remains rare.  In the developing world, cancer has a very different look, as illustrated in maps drawn by the World Health Organization’s International Agency for Cancer Research.  The countries with the highest incidence, like the United States, Canada, Australia and those of Western Europe, are dark blue. With the exception of South Africa, almost all of the African continent is light blue or white. The map could serve double duty — as a pointer to places with the highest standards of living and hence the longest life spans.  But that is just part of the story. Cancers that arise in poorer countries are far less likely to be survived.  A disproportionately large number of these cases are caused by infectious agents. Look again at the international maps, and pick the ones showing the worldwide incidence of cervical cancer, which is brought on by infection with the human papilloma virus.  This map is almost a reverse image of the ones for colorectal cancer or breast cancer — the leading cancers of the richer realms. For cervical cancer, the dark blues of trouble are concentrated in places like Mali, while the wealthier countries, with lower rates, are rendered in white.  This is a cancer that could practically be wiped out everywhere by the HPV vaccine, and those efforts are underway in poorer regions. Infection is also a major factor in stomach cancer and liver cancer. An Apollo-scale moon shot aimed at all of these killers would save millions of people who still have much of their lives to come.  As improvements in economic development and public health move forward, the disparities are evening out, as described in an update this week by epidemiologists at the American Cancer Society. Life expectancy will slowly increase, and rising alongside will be the overall cancer rate.  Cancers of the poor will gradually give way to cancers of the more affluent. They will move up the list of leading killers, replacing the old diseases.  This is already happening in countries like India, where more people are becoming overweight and living less active lives — risk factors for malignancies of the colon and breast. Women who forestall or forgo childbearing are also at higher risk for breast and other gynecological cancers.  More people are also able to afford a steady supply of cigarettes — and to live for the additional decades it takes for the cancerous mutations to pile up. China has joined North America and Europe as a hotbed of lung cancer, and other countries seem determined to catch up.  Dr. Vincent T. DeVita Jr., the renowned American oncologist, titled his new book “The Death of Cancer,” envisioning a time “when we’ll be able to cure almost all cancers” with an ever-improving stream of engineered pharmaceuticals and other cutting-edge treatments yet to be discovered.  Maybe that will happen, if we can afford it. But there are so many lower-tech, lower-cost and ultimately more heroic cancer moon shots yet to be made — ones that would save younger lives in Africa and throughout the world.  A version of this article appears in print on December 22, 2015, on page D3 of the New York edition with the headline: Cancer, Scourge of Affluent Nations. Order Reprints| Today's Paper|Subscribe
In the West, cancer often afflicts those who are affluent and older. In poorer countries, it is not even a leading cause of death.