Factors That Determine Multiple Primary Cancers in the Adult Population in the United States.

Cancer is a major public health problem worldwide and a leading cause of death in the United States. Multiple primary cancers mean that an individual has more than one cancer in the same or a different organ but does not include instances of metastasis of initial primary cancer. Several factors such as genetics, for example, gene mutations, may predict multiple primary cancers. Factors such as the age at first cancer diagnosis may determine the outcome of multiple primary cancers. This study aims to determine factors that determine multiple primary cancers among the adult population in the United States.  Methods: This study uses data from the Behavioral Risk Factor Surveillance System 2021 dataset. The study included all individuals recently diagnosed with cancer (sample size = 9806). All age groups were included in this study. Measures included the outcome variable number of cancers and a major independent variable: age at first cancer diagnosis. Covariates included race, sex, smoking status, and cancer treatment. Descriptive, bivariate, and multivariate logistic regressions were conducted using a statistical analysis system. It was hypothesized that individuals with age at first diagnosis of cancer at a younger age have higher odds of having multiple primary cancers as compared to individuals diagnosed at an older age.  Results: The age group of 50-64 years had the highest percentage of only one cancer type (35.87%) and of two or more cancers (35.46%). A majority of females had two or more cancers (53.52%) as compared to males (47.48%). The majority of participants with only one cancer type (80.59%) and two or more cancers (88.61%) were of White non-Hispanic ethnicity. At the multivariate level, the age group under 18 years had 9.4% higher odds of having two or more cancers compared to the age group of 18-29 years (adjusted OR (AOR)=1.094, 95%CI=1.026-1.166; p-value=0.0057). The age group 65 years and above had 11.6% lower odds of having multiple primary cancers as compared to the age group of 18-29 years (AOR=0.884; 95%CI=0.859-0910; p-value=<0.0001). The Black non-Hispanic group had 73.8% lower odds of having multiple primary cancers as compared to White non-Hispanic respondents (AOR= 0.262; 95%CI = 0.228-0.301; p-value = <0.0001). Hispanic respondents had 59.8% lower odds of having two or more cancers as compared to the White non-Hispanic group (AOR= 0.402; 95%CI=0.390-0.413; p-value=<0.0001). Current smokers had 9.7% higher odds of having multiple cancers as compared to individuals who never smoked (AOR = 1.097; 95%CI=1.066-1.129; p-value=<0.0001). Former smokers had 24.2% higher odds of having multiple cancers as compared to individuals who never smoked (AOR=1.242; 95%CI=1.224-1.261; p-value=<0.0001). Individuals who were currently on treatment had 2.676 higher odds of having two or more cancers as compared to individuals not on treatment (AOR=2.676; 95%CI=2.629-2.724; p-value=<0.0001).  Conclusion: Multiple primary cancers have been on the increase recently following advancements in anticancer therapy and cancer screening and diagnosis technology. It is important that studies that aim to demonstrate risk factors and predictors of multiple primary cancers such as the age at first diagnosis, smoking status, and cancer treatment are encouraged among public health specialists.