ACS: http://www.cancer.org/Cancer/CancerCauses/OtherCarcinogens/

GeneralInformationaboutCarcinogens/cancer-clusters

NIH: http://www.cancer.gov/cancertopics/factsheet/Risk/clusters

CDC: http://www.cdc.gov/nceh/clusters/

ATSDR: http://www.atsdr.cdc.gov/csem/cluster/docs/clusters.pdf

Harvard School of Public Health, Disease Risk Profile: http://www.diseaseriskindex.harvard.edu/update/hccpquiz.pl?lang=english&func=home&page=cancer_index