In the 1980s and 1990s, six former Amoco chemical engineers at the firm's Naperville, Illinois, research campus developed a deadly form of brain cancer. Researchers who conducted a three-year study of the cancer cluster determined that the cancer cases were workplace-related, but they could not identify the source of the workers' ailments. In June 2010, BP demolished Building 503, where the employees had worked. According to a company spokesperson, the building was "underused", and "required upgrades the company deemed too expensive." Heirs of one of the cancer-stricken workers won a $2.75 million suit against BP Amoco in 2000.