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WASHINGTON, July 15 (Reuters) - The American Cancer Society and three federal agencies named 19 chemicals and shift work on Thursday as potential causes of cancer that deserve more investigation.The group published a report with the backing of international experts who said the 20 potential causes they identified had fairly good evidence that they may be a danger and deserved more follow-up.Most are familiar names, such as chloroform, formaldehyde and polychlorinated biphenyls or PCBs, but the list includes indium phosphide, a relatively new compound used in making flat-screen televisions.All have been classified as possible carcinogens by the International Agency for Research on Cancer or IARC, the United Nations cancer agency."These particular ones were picked for two reasons. One is there is more of a hint in most cases that they might be involved with cancer," Elizabeth Ward of the American Cancer Society, who helped lead the work, said in a telephone interview.But at the same time, she said, the studies that could make a definitive link are missing.The second reason is that some of the potential agents or causes are very common. "We are focusing on things like formaldehyde, where there really has been widespread exposure in many industries," Ward said."Or in some cases the exposure is not widespread but is something that is increasing and there is insufficient data."The National Institute for Occupational Safety and Health or NIOSH, National Institute of Environmental Health Sciences and the National Cancer Institute also helped sponsor the report, which names the following agents:-Lead and lead compounds-Indium phosphide-Cobalt with tungsten carbide-Titanium dioxide-Welding fumes-Refractory ceramic fibers-Diesel exhaust-Carbon black-Styrene-7,8-oxide and styrene-Propylene oxide-Formaldehyde-Acetaldehyde-Dichloromethane, methylene chloride (DCM)-Trichloroethylene (TCE)-Tetrachloroethylene (perc, tetra, PCE)-Chloroform-Polychlorinated biphenyls (PCBs)-Di(2-ethylhexyl) phthalate (DEHP)-Atrazine-Shift workThe study is published in the journal Environmental Health Perspectives and at Ward said indium caught the group's attention because it is becoming increasingly common. Used to make microelectronics, animal data suggested it might cause lung damage and genetic changes when breathed in, she said."It is a particularly important component of the flat displays of TVs that have been so popular," she said. Workers in assembly plants and those recycling discarded televisions might be most at risk, she said."Some of this kind of work done is in developing countries," she noted. "They are broken apart and valuable components extracted. It is an example of a newly emerging hazard."Cancer is the No. 2 killer of Americans and people in most industrialized countries, after heart disease.In May the President's Cancer Panel said Americans are being "bombarded" with cancer-causing chemicals and radiation but many experts said it overplayed some causes for which there is very little evidence of a cancer-causing effect, such as cell phones.