Estimation of exposure distribution adjusting for association between exposure level and detection limit.

In environmental exposure studies, it is common to observe a portion of exposure measurements to fall below experimentally determined detection limits (DLs). The reverse Kaplan-Meier estimator, which mimics the well-known Kaplan-Meier estimator for right-censored survival data with the scale reversed, has been recommended for estimating the exposure distribution for the data subject to DLs because it does not require any distributional assumption. However, the reverse Kaplan-Meier estimator requires the independence assumption between the exposure level and DL and can lead to biased results when this assumption is violated. We propose a kernel-smoothed nonparametric estimator for the exposure distribution without imposing any independence assumption between the exposure level and DL. We show that the proposed estimator is consistent and asymptotically normal. Simulation studies demonstrate that the proposed estimator performs well in practical situations. A colon cancer study is provided for illustration. Copyright © 2017 John Wiley & Sons, Ltd.

Prevalence of human papillomavirus types in invasive cervical cancers from 7 US cancer registries before vaccine introduction.

OBJECTIVE: We conducted a baseline study of human papillomavirus (HPV) type prevalence in invasive cervical cancers (ICCs) using data from 7 cancer registries (CRs) in the United States. Cases were diagnosed between 1994 and 2005 before the implementation of the HPV vaccines. MATERIALS AND METHODS: Cancer registries from Florida, Kentucky, Louisiana, Michigan, Hawaii, Iowa, and Los Angeles, California identified eligible ICC cases and obtained sections from representative blocks of archived tumor specimens for DNA extraction. All extracts were assayed by linear array and, if inadequate or HPV negative, retested with INNO-LiPA Genotype test. Clinical and demographic factors were obtained from the CRs and merged with the HPV typing data to analyze factors associated with different types and with HPV negativity. RESULTS: A total of 777 ICCs were included in this analysis, with broad geographic, age, and race distribution. Overall, HPV was detected in 91% of cases, including 51% HPV-16, 16% HPV-18 (HPV-16-negative), and 24% other oncogenic and rare types. After HPV-16 and -18, the most common types were 45, 33, 31, 35, and 52. Older age and nonsquamous histology were associated with HPV-negative typing. CONCLUSIONS: This study provides baseline prevaccine HPV types for postvaccine ICC surveillance in the future. HPV-16 and/or -18 were found in 67% of ICCs, indicating the potential for vaccines to prevent a significant number of cervical cancers.

Concentrations of arsenic, chromium, and nickel in toenail samples from Appalachian Kentucky residents.

Lung cancer rates in Appalachian Kentucky are almost twice national rates; colorectal cancer rates are also elevated. Although smoking prevalence is high, it does not explain all excess risk. The area is characterized by poverty, low educational attainment, and unemployment. Coal production is a major industry. Pyrite contaminants of coal contain established human carcinogens, arsenic (As), chromium (Cr), and nickel (Ni). We compared biological exposure to As, Cr, and Ni for adults living in Appalachian Kentucky with residents of Jefferson, a non-Appalachian, urban county. We further compared lung and colon cancer rates, demographics, and smoking prevalence across the study areas. Toenail clipping analysis measured As, Cr, and Ni for residents of 23 rural Appalachian Kentucky counties and for Jefferson County. Reverse Kaplan-Meier statistical methodology addressed left-censored data. Appalachian residents were exposed to higher concentrations of As, Cr, and Ni than Jefferson County residents. Lung cancer incidence and mortality rates in Appalachia are higher than Jefferson County and elsewhere in the state, as are colorectal mortality rates. Environmental factors may contribute to the increased concentration of trace elements measured in residents of the Appalachian region. Routes of human exposure need to be determined.