In rural China, where about 41 percent of the population lives, only about one-fifth of cancer patients survive five years past their diagnosis. In urban areas, about 40 percent survive, according to China’s National Cancer Prevention and Research Center. In the United States, by comparison, more than two-thirds survive through that period.

Tang Gongwei’s disappearance was widely reported in the Chinese media, with some outlets mistakenly saying that he was a doctor. The fact that he was a medical professional fueled the discussion about him online, and many internet users said they would also have left because they didn’t want to burden their own parents.

Like many other Chinese children, Tang Gongwei grew up without siblings. Local officials enforced family planning rules zealously, tearing down houses of couples who had more than one child, according to his mother, Liao Mandong.

“At least if you gave birth to a girl, you were allowed to have another one,” she said. China’s one-child policy allowed rural residents to have a second child if the first one was a girl, unlike their counterparts living in urban areas.