Family size can affect cancer risk
Researchers discover a stomach cancer often afflicts younger kids in large families
Younger children in large families appear most susceptible to a common type of stomach cancer, researchers found in studies of a group of Japanese- American men in Hawaii.
The subjects were part of a cohort of 8,006 Japanese-American men recruited in 1965 for the Honolulu Heart Program, based at Kuakini Medical Center. They were born from 1900 through 1919 and identified through the World War II Selective Service registration file.
Many health and aging studies have been done over the years on the men, with data gathered from interviews, examinations and records.
Dr. Abraham Nomura, who has retired from Kuakini Medical Center and the Cancer Research Center of Hawaii, led the initial heart program. An epidemiologist, he has participated in a series of studies on stomach cancer, including the latest one reported in Tuesday's online issue of Public Library of Science Medicine.
The researchers found that family size and the order of birth influenced development of stomach cancer linked to Helicobacter pylori bacteria, Nomura said.
The bacteria, also associated with ulcers and gastritis, can live for decades in the stomach's mucous layer, the investigators said.
Half the people in the world are estimated to carry the bacteria in their stomach. According to medical literature, it is acquired through contaminated food or water or person-to-person contact. It is common in people who live in crowded or unsanitary conditions.
Since more people are involved in large families and more interaction is going on, Nomura said, "The tendency is for younger children to be infected at an earlier age."
"The situation has improved over time with better hygiene," he said, "plus now family size has gotten smaller."
Comparing the men in the study who were born in Japan and came here with those who were born here, Nomura said, "The ones born here had lower prevalence of passing the infection. With each succeeding generation and smaller family sizes, fewer people are infected."
Dr. Martin J. Blaser, professor and chairman of the Department of Medicine and professor of microbiology at New York University, led the study.
Other authors besides Nomura were Blaser's longtime associate Dr. Guillermo Perez-Perez, NYU associate professor of medicine and microbiology; Dr. Grant Stemmermann, former chief of pathology at Kuakini Medical Center; and James Lee, Kuakini biostatistician.
Blaser and his colleagues published a study in the mid-1990s in the New England Journal of Medicine on the relationship between H. pylori and stomach cancer and an associated gene called cagA.
Blood samples were banked from 7,429 of the Japanese-American men examined between 1967 and 1975, and 261 developed cancer in the following years.
Extending their follow-up of the cohort to 28 years, the investigators went back to the blood samples of the men who developed cancer and tested them for antibodies to the H. pylori bacteria and cagA protein, NYU Medical Center reported.
The men with cancer were three times more likely to carry the bacteria than those who did not have cancer, and they had large numbers of siblings, the researchers found.
Blaser said the study "clearly shows there are factors in early childhood that affect the risk of developing cancer many years later," according to the NYU report.
"That early childhood events affect the risk of cancers occurring in old age is remarkable, and this may be a model for other cancers."
Blaser suggests younger children in large families could acquire the bacteria from older siblings when their immune systems are still developing. Since the bacteria has already adapted to an older sibling, it has a "head start" in the younger child, he said.
"This sets the stage for a more virulent, better adapted bacterial population than would occur otherwise if the bacterium was transmitted from a genetically unrelated individual," he said.