Background: Little is known in human immunodeficiency virus (HIV)–positive women about how the combination of plasma HIV RNA level and CD4 ⁺ T-cell count is associated with the natural history of human papillomavirus (HPV) infection or about HPV reactivation—whether it occurs and with what frequency in HIV-positive women. Methods: HIV-positive (n = 1848) and -negative (n = 514) women were assessed at semiannual visits (total person-years = 5661) for cervicovaginal HPV with polymerase chain reaction assays and for squamous intraepithelial lesions (SILs) by Pap smear. We studied the prevalent detection of HPV and SILs with generalized estimating equations and the incident detection and persistence of HPV and SILs with multivariable Cox models. All statistical tests were two-sided. Results: We observed a strong interaction between the associations of CD4 ⁺ and plasma HIV RNA strata with both prevalent ( P_interaction = .002) and incident ( P_interaction = .001) detection of HPV. Indeed, the hazard ratio for incident HPV detection peaked between 4.0 and 5.0, with either a CD4 ⁺ count of less than 200 cells per mm ³ or an HIV RNA level of more than 100 000 copies per mL. Although incident HPV detection in all women was associated with the number of recent sex partners ( P_trend <.001), 22% of sexually inactive HIV-positive women with a CD4 ⁺ count of less than 200 cells/mm ³ also had at least one incidently detected HPV type. The association between CD4 ⁺ /HIV RNA strata and HPV persistence was statistically significantly smaller ( P <.001) than for incident HPV detection. SIL prevalence, incident detection, and persistence had similar associations with CD4 ⁺ /HIV RNA strata as HPV (above). Conclusion: In HIV-positive women, plasma HIV RNA level and CD4 ⁺ count in combination appear to have a strong and statistically interactive association with incident detection of HPV, some of which may reflect HPV reactivation (e.g., in sexually inactive women). The more moderate association between HIV coinfection and HPV persistence could partly explain why cervical cancer rates have not reached more epidemic proportions in HIV-positive women.

Background: Human papillomavirus (HPV) type 16 is etiologically associated with approximately half of all cervical cancers. It is important, therefore, to determine the characteristics that distinguish HPV16 from other HPV types. A preliminary result based on cross-sectional baseline data in the Women’s Interagency Human Immunodeficiency Virus (HIV) Study (WIHS) suggested that the prevalence of HPV16 might have a weaker association with immune status in HIV-seropositive women than that of other HPV types. To address this issue, we examined HPV test results from repeated study visits in the WIHS and from an independent study, the HIV Epidemiology Research Study (HERS). Methods: HIV-seropositive women in the WIHS (n = 2058) and in the HERS (n = 871) were assessed semiannually. HPV DNA was detected in cervicovaginal lavage specimens by using polymerase chain reaction assays. Prevalence ratios were used to compare the prevalence of each HPV type in women with the lowest CD4+ T-cell counts (<200 T cells/mm³) with that of women with the highest CD4+ T-cell counts (⩾500 T cells/mm³). A summary prevalence ratio for each HPV type (i.e., across visits and studies) was estimated using generalized estimating equations. The association of CD4+ T-cell stratum with type-specific HPV incidence was measured using multivariable Cox regression models. All statistical tests were two-sided. Results: The prevalence ratio for HPV16 was low compared with that of other HPV types at every study visit in both cohorts. The generalized estimating equation summary prevalence ratio for HPV16 (1.25, 95% confidence interval [CI] = 0.97 to 1.62) was the smallest measured, and it was statistically significantly lower than that of all other HPV types combined (P = .01). The association of CD4+ T-cell stratum with HPV16 incidence was also among the smallest measured (hazard ratio = 1.69, 95% CI = 1.01 to 2.81). Conclusions: The prevalent and incident detection of HPV16 is more weakly associated with immune status in HIV-seropositive women than that of other HPV types, suggesting that HPV16 may be better at avoiding the effects of immune surveillance, which could contribute to HPV16’s strong association with cervical cancer.

Purpose: Emerging evidence suggests that metformin may reduce breast cancer incidence, but reports are mixed and few provide information on tumor characteristics. Therefore, we assessed associations among diabetes, metformin use, and breast cancer in postmenopausal women participating in Women's Health Initiative clinical trials. Patients and Methods: In all, 68,019 postmenopausal women, including 3,401 with diabetes at study entry, were observed over a mean of 11.8 years with 3,273 invasive breast cancers diagnosed. Diabetes incidence status was collected throughout follow-up, with medication information collected at baseline and years 1, 3, 6, and 9. Breast cancers were confirmed by review of central medical records and pathology reports. Cox proportional hazards regression, adjusted for breast cancer risk factors, compared breast cancer incidence in women with diabetes who were metformin users or nonusers with breast cancer incidence in women without diabetes. Results: Compared with that in women without diabetes, breast cancer incidence in women with diabetes differed by diabetes medication type (P = .04). Women with diabetes receiving medications other than metformin had a slightly higher incidence of breast cancer (hazard ratio [HR], 1.16; 95% CI, 0.93 to 1.45), and women with diabetes who were given metformin had lower breast cancer incidence (HR, 0.75; 95% CI, 0.57 to 0.99). The association was observed for cancers positive for both estrogen receptor and progesterone receptor and those that were negative for human epidermal growth factor receptor 2. Conclusion: Metformin use in postmenopausal women with diabetes was associated with lower incidence of invasive breast cancer. These results can inform future studies evaluating metformin use in breast cancer management and prevention.

Case-cohort studies have become common in epidemiological studies of rare disease, with Cox regression models the principal method used in their analysis. However, no appropriate procedures to assess the assumption of proportional hazards of case-cohort Cox models have been proposed. We extended the correlation test based on Schoenfeld residuals, an approach used to evaluate the proportionality of hazards in standard Cox models. Specifically, pseudolikelihood functions were used to define “case-cohort Schoenfeld residuals”, and then the correlation of these residuals with each of three functions of event time (i.e., the event time itself, rank order, Kaplan-Meier estimates) was determined. The performances of the proposed tests were examined using simulation studies. We then applied these methods to data from a previously published case-cohort investigation of the insulin/IGF-axis and colorectal cancer. Simulation studies showed that each of the three correlation tests accurately detected non-proportionality. Application of the proposed tests to the example case-cohort investigation dataset showed that the Cox proportional hazards assumption was not satisfied for certain exposure variables in that study, an issue we addressed through use of available, alternative analytical approaches. The proposed correlation tests provide a simple and accurate approach for testing the proportional hazards assumption of Cox models in case-cohort analysis. Evaluation of the proportional hazards assumption is essential since its violation raises questions regarding the validity of Cox model results which, if unrecognized, could result in the publication of erroneous scientific findings.

IGF-I shares structural homology and in vitro metabolic activity with insulin. Laboratory models suggest that IGF-I and its binding proteins IGFBP-1 and IGFBP-2 have potentially beneficial effects on diabetes risk, whereas IGFBP-3 may have adverse effects. We therefore conducted a prospective nested case-control investigation of incident diabetes (n = 742 case subjects matched 1:1 to control subjects) and its associations with IGF-axis protein levels in the Nurses’ Health Study, a cohort of middle-aged women. The median time to diabetes was 9 years. Statistical analyses were adjusted for multiple risk factors, including insulin and C-reactive protein. Diabetes risk was fivefold lower among women with baseline IGFBP-2 levels in the top versus bottom quintile (odds ratio [OR]_q5–q1 = 0.17 [95% CI 0.08–0.35]; P trend < 0.0001) and was also negatively associated with IGFBP-1 levels (OR_q5–q1 = 0.37 [0.18–0.73]; P trend = 0.0009). IGFBP-3 was positively associated with diabetes (OR_q5–q1 = 2.05 [1.20–3.51]; P trend = 0.002). Diabetes was not associated with total IGF-I levels, but free IGF-I and diabetes had a significant association that varied (P interaction = 0.003) by insulin levels above the median (OR_q5–q1 = 0.48 [0.26–0.90]; P trend = 0.0001) versus below the median (OR_q5–q1 = 2.52 [1.05–6.06]; P trend < 0.05). Thus, this prospective study found strong associations of incident diabetes with baseline levels of three IGFBPs and free IGF-I, consistent with hypotheses that the IGF axis might influence diabetes risk.

Increasing evidence indicates that individuals with type 2 diabetes (diabetes) are at elevated risk for several common human malignancies, including cancers of the colon, breast, endometrium, pancreas, and liver. In particular, the consistent positive results reported by prospective investigations make it unlikely that methodologic issues, occult tumors, or chance results could explain the findings. Since diabetes and impaired fasting glucose together affect >25% of Americans above age 50, even a moderate etiologic association (e.g., relative risk = 1.5) would explain >10% of involved malignancies. Laboratory studies have suggested biologically plausible mechanisms. Insulin, for example, is typically at high levels during the development and early stages of diabetes. Activation of the insulin receptor by its ligand, or cross-activation of the insulin-like growth factor–I receptor, has been shown to be mitogenic and promote tumorigenesis in various model systems. A "unifying concept," in fact, holds that hyperinsulinemia may underlie the cancer associations of several additional risk factors, including high waist circumference, visceral fat, waist-to-hip ratio, body mass index, sedentary lifestyle, and energy intake. In this review, we assess current evidence regarding the relation of type 2 diabetes with cancer, and evaluate the findings in terms of well-accepted criteria for establishing causality.