A parallel analysis of cancer mortality among atomic bomb survivors and patients with ankylosing spondylitis given X-ray therapy.

Radiation-induced cancer mortality rates among atomic bomb survivors with doses of at least 100 rad and patients with ankylosing spondylitis given X-ray therapy have been compared for the first time. The estimated average mean bone marrow dose for the spondylitics is more than twice that for atomic bomb survivors, and yet spondylitics experienced only half the risk of radiation-induced leukemia of atomic bomb survivors. For sites that were heavily irradiated in the spondylitics, provisional estimates indicate comparable doses in the two studies, and similar levels of cancer risk were observed. For these sites, when information from the studies was combined, there were statistically significant excesses for cancers of the esophagus, stomach, lung, and ovaries, multiple myeloma, other lymphomas, and tumors of the spinal cord and nerves. Very high relative risks (RR's) for tumors of the spinal cord and nerves were observed in both studies. For sites that were lightly irradiated in the spondylitics, in addition to previously documented sites, there was a statistically significant excess of cancers of the liver and gallbladder among atomic bomb survivors. A previous subdivision of cancer sites into radiosensitive and other tissues was not supported by the atomic bomb survivor data. Changes in the rates of radiation-induced cancers with age at exposure and time since exposure were studied and compared with the use of generalized linear modeling of the RR's and also by examination of the excess mortality rates. The level of agreement between the two studies was high; provided it is accepted that the reduced level of leukemia risk in the spondylitics is due to cell sterilization, no inconsistencies were found. For a group of solid tumors selected from heavily irradiated sites in the spondylitics, excess risk increased with both age at exposure and time since exposure and RR decreased with age at exposure, but it did not vary with time since exposure between about 5 and at least 30 years following exposure. The finding of a constant RR with time since exposure did not extend to all remaining neoplasms other than leukemia, because the RR for these neoplasms increased with time since exposure in atomic bomb survivors.