Subtype-specific risk factors for postmenopausal breast cancer: findings from the PLCO trial.

OBJECTIVE: The aim of this analysis is to evaluate the relative weight of different epidemiological risk factors on the development of different breast cancer subtypes (i.e. luminal, Her2+ overexpressed or triple negative). METHODS: De-identified datasets of female participants recruited within the Prostate, Lung, Colorectal, and Ovarian (PLCO) trial were accessed. Multivariate Cox regression analysis was utilized to assess factors affecting the development of breast cancer (regardless of subtype). Additional multivariate analyses were conducted to assess factors affecting the development of the three principal subtypes of breast cancer (ER+/Her2- breast cancer; Her2 overexpressed breast cancer and ER-/Her2- breast cancer). RESULTS: A total of 73,570 eligible participants were evaluated in the current analysis of which 2370 participants subsequently developed breast cancer. The following factors were associated with a higher risk of ER+/Her2- breast cancer: white race (P < 0.001), nulliparity (P < 0.001), higher body mass index (P = 0.003), prior exposure to hormone treatment (P = 0.004) and breast cancer in first-degree female relatives (P < 0.001). The following factors were associated with a higher risk of Her2 overexpressed breast cancer: prior exposure to hormone treatment (P = 0.002) and breast cancer in first-degree female relatives (P = 0.001). The following factors were associated with a higher risk of ER-/Her2- breast cancer: black race (P = 0.013), younger age (P = 0.017) and breast cancer in first-degree female relatives (P 0.023). CONCLUSIONS: There is considerable heterogeneity in risk factors among patients with different subtypes of breast cancer. In particular, factors associated with high estrogen levels seem to be associated with luminal breast cancer rather than other breast cancer subtypes.

An Examination of Lymph Node Sampling as a Predictor of Survival in Resected Node-Negative Small Bowel Adenocarcinoma: a SEER Database Analysis.

BACKGROUND: Small bowel adenocarcinoma (SBA) is a rare disease. Current recommendations are largely extrapolated from the colorectal literature. For node-negative (N -ve) cases, optimally stratifying cases into high or low risk, may help define optimal management. The objective of this analysis was to determine the importance of lymph node sampling for prognostication and to define what number of lymph nodes sampled is adequate. METHODS: Cases of non-metastatic SBA with complete staging, pathologic, and demographic information were selected from the SEER database and SAS 9.4 software was used. Variables included age, gender, race, grade, TNM staging, and number of lymph nodes were examined. Comparisons were made between N -ve and N +ve cases. Survival analysis using N -ve cases was performed to characterize the impact of nodal sampling on survival and to determine which nodal cut-offs best predict survival. RESULTS: A total of 523 cases from 2004 to 2014 were included in this analysis. Statistically significant differences identified included the median number of nodes sampled between the N -ve and N +ve groups, and the distribution of T stage and grade. Survival analysis in the N -ve cases demonstrated that the strongest predictor of survival was sampling of 16 or more lymph nodes. CONCLUSION: In this analysis, lymph node sampling was shown to be the most important pathologic predictor of survival in cases of N -ve SBA. Replicating these findings in a secondary dataset and determining whether a clinical benefit of adjuvant chemotherapy exists for SBA patients with inadequate sampling are both important next steps.

Epidermal growth factor receptor inhibitor-induced hypomagnesemia: a survey of practice patterns among Canadian gastrointestinal medical oncologists.

Background: The optimal management of hypomagnesemia (hMg) induced by epidermal growth factor receptor inhibitors (egfris) for advanced colorectal cancer is unclear. We surveyed gastrointestinal medical oncologists in Canada to determine practice patterns for the management of egfri-induced hMg. Methods: Based on distribution lists from the Eastern Canadian Colorectal Cancer Consensus Conference and the Western Canadian Gastrointestinal Cancer Consensus Conference, medical oncologists were invited to participate in an online questionnaire between November 2013 and February 2014. Results: From the 104 eligible physicians, 40 responses were obtained (38.5%). Panitumumab was more commonly prescribed than cetuximab by 70% of respondents, with 25% prescribing cetuximab and panitumumab equally. Most respondents obtain a serum magnesium level before initiating a patient on an egfri (92.5%) and before every treatment (90%). Most use a reactive strategy for magnesium supplementation (90%) and, when using supplementation, favour intravenous (iv) alone (40%) or iv and oral (45%) dosing. Magnesium sulfate was used for iv replacement, and the most common oral strategies were magnesium oxide (36.4%) and magnesium rougier (18.2%). Under the reactive strategy, intervention occurred at hMg grade 1 (70.3%) or grade 2 (27%). Of the survey respondents, 45% felt that 1-5 of their patients have ever developed symptoms attributable to hMg, and 35% have had to interrupt egfri therapy because of this toxicity, most commonly at grade 3 (30%) or grade 4 (45%) hMg. The most important question about egfri-induced hMg was its relevance to clinical outcomes (45%) and its symptoms (37.5%). Conclusions: In Canada, various strategies are used in the management of egfri-induced hMg, including prophylactic and reactive approaches that incorporate iv, oral, or a combination of iv and oral supplementation. Clinicians are concerned about the effect of hMg on clinical outcomes and about the symptoms that patients experience as a result of this toxicity.

What is a clinically meaningful survival benefit in refractory metastatic colorectal cancer?

Assessment of the clinical benefit of cancer treatments can be highly subjective, influenced by both perspective and context. Such assessments are required in regulatory and policy decision-making, but consistency between jurisdictions is often lacking. Clear and consistent standards for determining when a treatment offers a meaningful benefit, relative to the current standard of care, can help to address issues of equity and transparency in health technology assessment. For metastatic colorectal cancer (mcrc), no standardized Canadian definition of clinically meaningful benefit has yet been proposed. Colorectal Cancer Canada therefore convened a group of medical oncologists expert in colorectal cancer to review the literature about clinical significance. The resulting consensus is intended to apply to any therapeutic agent being considered in the setting of chemotherapy-refractory mcrc. It was agreed that overall survival is the appropriate measure of clinical efficacy in chemorefractory mcrc. As quantitative targets for efficacy, an improvement of 2 months or more in median overall survival or a hazard ratio for survival of 0.75 or lower (or both) are proposed as the threshold for clinically meaningful benefit. That threshold could be influenced by a treatment's effect on quality of life. Treatment toxicity is also relevant to the assessment of clinical benefit in this setting, specifically when significant differences in treatment tolerability are evident.

Opportunity is the greatest barrier to providing palliative care to advanced colorectal cancer patients: a survey of oncology clinicians.

Palliative care (pc) is part of the recommended standard of care for patients with advanced cancer. Nevertheless, delivery of pc is inconsistent. Patients who could benefit from pc services are often referred late-or not at all. In planning for improvements to oncology pc practice in our health care system, we sought to identify barriers to the provision of earlier pc, as perceived by health care providers managing patients with metastatic colorectal cancer (mcrc). We used the Michie Theoretical Domains Framework (tdf) and Behaviour Change Wheel (bcw), together with knowledge of previously identified barriers, to develop a 31-question survey. The survey was distributed by e-mail to mcrc health care providers, including physicians, nurses, and allied staff. Responses were obtained from 57 providers (40% response rate). The most frequently cited barriers were opportunity-related-specifically, lack of time, of clinic space for consultations, and of access to specialist pc staff or services. Qualitative responses revealed that resource limitations varied by cancer centre location. In urban centres, time and space were key barriers. In rural areas, access to specialist pc was the main limiter. Self-perceived capability to manage pc needs was a barrier for 40% of physicians and 30% of nurses. Motivation was the greatest facilitator, with 89% of clinicians perceiving that patients benefit from pc. Based on the Michie tdf and bcw model, interventions that best address the identified barriers are enablement and environmental restructuring. Those findings are informing the development of an intervention plan to improve oncology pc practices in a publicly funded health care system.

Risk and predictors of suicide in colorectal cancer patients: a Surveillance, Epidemiology, and End Results analysis.

BACKGROUND: The risk of suicide is higher for patients with colorectal cancer (crc) than for the general population. Given known differences in morbidity and sites of recurrence, we sought to compare the predictors of suicide for patients with colon cancer and with rectal cancer. METHODS: Using the U.S. Surveillance, Epidemiology, and End Results database, adult patients with confirmed adenocarcinoma of the colon or rectum during 1973-2009 were identified. Parametric and nonparametric tests were used to assess selected variables, and Cox proportional hazards regression models were used to determine predictors of suicide. RESULTS: The database identified 187,996 patients with rectal cancer and 443,368 with colon cancer. Compared with the rectal cancer group, the colon cancer group was older (median age: 70 years vs. 67 years; p < 0.001) and included more women (51% vs. 43%, p < 0.001). Suicide rates were similar in the colon and rectal cancer groups [611 (0.14%) vs. 337 (0.18%), p < 0.001]. On univariate analysis, rectal cancer was a predictor of suicide [hazard ratio (hr): 1.26; 95% confidence interval (ci): 1.10 to 1.43]. However, after adjusting for clinical and pathology factors, rectal cancer was not a predictor of suicide (hr: 1.05; 95% ci: 0.83 to 1.33). In the colon cancer cohort, independent predictors of suicide included older age, male sex, white race, and lack of primary resection. The aforementioned predictors, plus metastatic disease, similarly predicted suicide in the rectal cancer cohort. CONCLUSIONS: The suicide risk in crc patients is low (<0.2%), and no difference was found based on location of the primary tumour. Sex, age, race, distant spread of disease, and intact primary tumour were the main predictors of suicide among crc patients. Further studies and interventions are needed to target these high-risk groups.

Randomized phase II study of modified FOLFOX-6 in combination with ramucirumab or icrucumab as second-line therapy in patients with metastatic colorectal cancer after disease progression on first-line irinotecan-based therapy.

BACKGROUND: Icrucumab and ramucirumab are recombinant human IgG1 monoclonal antibodies that bind VEGF receptors 1 and 2 (VEGFR-1 and -2), respectively. This randomized phase II study evaluated the antitumor activity and safety of icrucumab and ramucirumab each in combination with mFOLFOX-6 in patients with metastatic colorectal cancer after disease progression on first-line therapy with a fluoropyrimidine and irinotecan. PATIENTS AND METHODS: Eligible patients were randomly assigned to receive mFOLFOX-6 alone (mFOLFOX-6) or in combination with ramucirumab 8 mg/kg IV (RAM+mFOLFOX-6) or icrucumab 15 mg/kg IV (ICR+mFOLFOX-6) every 2 weeks. Randomization was stratified by prior bevacizumab therapy. The primary end point was progression-free survival (PFS). Secondary end points included overall survival (OS), tumor response, safety, and PK. RESULTS: In total, 158 patients were randomized, but only 153 received treatment (49 on mFOLFOX-6, 52 on RAM+mFOLFOX-6, and 52 on ICR+mFOLFOX-6). Median PFS was 18.4 weeks on mFOLFOX-6, 21.4 weeks on RAM+mFOLFOX-6, and 15.9 weeks on ICR+mFOLFOX-6 (RAM+mFOLFOX-6 versus mFOLFOX-6, stratified hazard ratio [HR] 1.116 [95% CI 0.713-1.745], P = 0.623; ICR+mFOLFOX-6 versus mFOLFOX-6, stratified HR 1.603 [95% CI 1.011-2.543], P = 0.044). Median survival was 53.6 weeks on mFOLFOX-6, 41.7 weeks on RAM+mFOLFOX-6, and 42.0 weeks on ICR+mFOLFOX-6. The most frequent adverse events reported on the ramucirumab arm (RAM+mFOLFOX-6) were fatigue, nausea, and peripheral sensory neuropathy; those on the icrucumab arm (ICR+mFOLFOX-6) were fatigue, diarrhea, and peripheral sensory neuropathy. Grade ≥3 serious adverse events occurred at comparable frequency across arms. CONCLUSIONS: In this study population, combining ramucirumab or icrucumab with mFOLFOX-6 did not achieve the predetermined improvement in PFS. CLINICALTRIALSGOV: NCT01111604.

Estimation of drug cost avoidance and pathology cost avoidance through participation in NCIC Clinical Trials Group phase III clinical trials in Canada.

BACKGROUND: Cost avoidance occurs when, because of provision of a drug therapy [drug cost avoidance (dca)] or a pathology test [pathology cost avoidance (pca)] during trial participation, health care payers need not pay for standard treatments or testing. The aim of our study was to estimate the total dca and pca for Canadian patients enrolled in relevant phase iii trials conducted by the ncic Clinical Trials Group. METHODS: Phase iii trials that had completed accrual and resulted in dca or pca were identified. The pca was calculated based on the number of patients screened and the test cost. The dca was estimated based on patients randomized, the protocol dosing regimen, drug cost, median dose intensity, and median duration of therapy. Costs are presented in Canadian dollars. No adjustment was made for inflation. RESULTS: From 1999 to 2011, 4 trials (1479 patients) resulted in pca and 17 trials (3195 patients) resulted in dca. The total pca was estimated at $4,194,849, which included testing for KRAS ($141,058), microsatellite instability ($18,600), and 21-gene recurrence score ($4,035,191). The total dca was estimated at $27,952,512, of which targeted therapy constituted 43% (five trials). The combined pca and dca was $32,147,361. CONCLUSIONS: Over the study period, trials conducted by the ncic Clinical Trials Group resulted in total cost avoidance (pca and dca) of approximately $7,518 per patient. Although not all trials lead to cost avoidance, such savings should be taken account when the financial impact of conducting clinical research is being considered.

Clinical outcomes of elderly patients receiving neoadjuvant chemoradiation for locally advanced rectal cancer.

BACKGROUND: Studies of clinical outcomes of elderly patients treated with neoadjuvant chemoradiation (nCRT) for locally advanced rectal cancer (LARC) are limited. Our aim was to assess the impact of age on clinical outcomes in a large multi-institutional database. PATIENTS AND METHODS: Data for patients diagnosed with LARC who received nCRT and curative-intent surgery between 2005 and 2012 were collected from five major Canadian cancer centers. Age was analyzed as a continuous and dichotomous variable (< 70 versus ≥ 70 years) and correlated with disease-free survival (DFS), cancer-specific survival (CSS) and overall survival (OS). Cox regression models were used to adjust for important prognostic factors. RESULTS: Of 1172 patients included, 295 (25%) were ≥ 70 years, and they were less likely to receive adjuvant chemotherapy (ACT; 60% versus 79%, P < 0.0001), oxaliplatin-based ACT (12% versus 31%, P < 0.0001), less likely to complete nCT (76% versus 86%, P < 0.001), and more likely to be anemic at initiation of nCRT (42% versus 30%, P = 0.0004). In multivariate analyses, age ≥ 70 years was associated with similar DFS [hazard ratio (HR) 0.93, 95% confidence interval (CI) 0.68-1.26, P = 0.63], similar CSS (HR 0.81, 95% CI 0.46-1.41, P = 0.45), and similar OS (HR 1.28, 95% CI 0.88-1.86, P = 0.20), compared with the younger age group. As a continuous variable, increasing age was not predictive of DFS (HR 1.00, 95% CI 0.99-1.02, P = 0.49) or CSS (HR 1.002, 95% CI 0.98-1.02, P = 0.88); however, it correlated with an inferior OS (HR 1.02, 95% CI 1.00-1.03, P = 0.04). CONCLUSIONS: Elderly patients (≥ 70 years) who receive nCRT followed by surgery appear to have similar outcomes compared with younger patients. Decisions regarding eligibility for nCRT and surgery should not be based on age alone.

Factors associated with publication of randomized phase iii cancer trials in journals with a high impact factor.

BACKGROUND: Impact factor (if) is often used as a measure of journal quality. The purpose of the present study was to determine whether trials with positive outcomes are more likely to be published in journals with higher ifs. METHODS: We reviewed 476 randomized phase iii cancer trials published in 13 journals between 1995 and 2005. Multivariate logistic regression models were used to investigate predictors of publication in journals with high ifs (compared with low and medium ifs). RESULTS: A positive outcome had the strongest association with publication in high-if journals [odds ratio (or): 4.13; 95% confidence interval (ci): 2.67 to 6.37; p < 0.001]. Other associated factors were a larger sample size (or: 1.06; 95% ci: 1.02 to 1.10; p = 0.001), intention-to-treat analysis (or: 2.53; 95% ci: 1.56 to 4.10; p < 0.001), North American authors (or for European authors: 0.36; 95% ci: 0.23 to 0.58; or for international authors: 0.41; 95% ci: 0.20 to 0.82; p < 0.001), adjuvant therapy trial (or: 2.58; 95% ci: 1.61 to 4.15; p < 0.001), shorter time to publication (or: 0.84; 95% ci: 0.77 to 0.92; p < 0.001), uncommon tumour type (or: 1.39; 95% ci: 0.90 to 2.13; p = 0.012), and hematologic malignancy (or: 3.15; 95% ci: 1.41 to 7.03; p = 0.012). CONCLUSIONS: Cancer trials with positive outcomes are more likely to be published in journals with high ifs. Readers of medical literature should be aware of this "impact factor bias," and investigators should be encouraged to submit reports of trials of high methodologic quality to journals with high ifs regardless of study outcomes.

A phase II study of erlotinib in gemcitabine refractory advanced pancreatic cancer.

BACKGROUND: Erlotinib induced skin toxicity has been associated with clinical benefit in several tumour types. This phase II study evaluated the efficacy of erlotinib, dose escalated to rash, in patients with advanced pancreatic cancer previously treated with gemcitabine. METHODS: Erlotinib was given at an initial dose of 150 mg/day, and the dose was escalated by 50mg every 2 weeks (to a maximum of 300 mg/day) until >grade 1 rash or other dose limiting toxicities occurred. Erlotinib pharmacokinetics were performed, and baseline tumour tissue was collected for mutational analysis and epidermal growth factor receptor (EGFR) expression. The primary end-point was the disease control rate (objective response and stable disease >8 weeks). RESULTS: Fifty-one patients were accrued, and 49 received treatment. Dose-escalation to 200-300 mg of erlotinib was possible in 9/49 (18%) patients. The most common ⩾ grade 3 adverse events included fatigue (6%), rash (4%) and diarrhoea (4%). Thirty-seven patients were evaluable for response, and the best response was stable disease in 12 patients (32% (95% confidence interval (CI) 17-47%)). Disease control was observed in nine patients (24% (95% CI: 10-38%)). Median survival was 3.8 months, and 6 month overall survival rate was 32% (95% CI 19-47%). Mutational analysis and EGFR expression were performed on 29 patients, with 93% having KRAS mutations, none having EGFR mutations, and 86% expressing EGFR. Neither KRAS mutational status nor EGFR expression was associated with survival. CONCLUSIONS: Erlotinib dose escalated to rash was well tolerated but not associated with significant efficacy in non-selected patients with advanced pancreatic cancer.

Characterization of published errors in high-impact oncology journals.

PURPOSE: To assess the frequency and propagation rate of published errors in the oncology literature and to determine possible contributing factors. METHODS: We reviewed 10 major oncology journals to determine variability in the online presentation of errata. Canadian oncologists were surveyed regarding characteristics that may influence error propagation. Errors published during 2004-2007 in the Journal of Clinical Oncology (jco) and the Journal of the National Cancer Institute (jnci) were classified as trivial or serious (that is, whether change in outcome was involved). The frequency of citation and error propagation was determined for serious errors. RESULTS: Of the 10 journals reviewed, 9 present links from the original article to the erratum; in 4 of those 9 journals, at least 1 link was missing. Survey results indicate that 33% of oncologists do not read errata, and 45% have read only the abstract when referencing an article. Although 59% of oncologists have noticed errors in cancer publications, only 13% reported the error. Together, jco and jnci published 190 errata, for an error rate of 4% ± 1% (standard deviation) annually; 26 of 190 errors were serious (14%). The median time from publication of the article to the corresponding erratum was 3.5 months for trivial errors as compared with 8.3 months for serious errors (p = 0.03). Error propagation in citations before and after publication of the erratum was 15% and 2% respectively (p < 0.01). CONCLUSIONS: Error rates in high-impact oncology journals average 4%, which is likely an underestimate, because errors noticed by readers are not consistently reported. Propagation of serious errors decreases, but still continues, after publication of errata.

Influence of an independent review committee on assessment of response rate and progression-free survival in phase III clinical trials.

BACKGROUND: Our objective was to determine the variability in assessment between investigators (INV) and independent review committees (IRC) for response rate (RR) and progression-free survival (PFS). METHODS: Phase III trials reporting INV and IRC assessments were identified. The difference in end point assessment (IRC - INV) across all study arms was determined. A random-effects model was used to calculate the mean difference between INV and IRC RR as well as PFS. Differences in estimated benefits of treatment (experimental - control) between IRC and INV were determined. RESULTS: Twenty-one trials were included (18 RR, 8 PFS). The estimated mean difference between IRC- and INV-determined RR was 4.57% [95% confidence interval (CI) 2.95% to 6.19%]. For median PFS, the estimated mean difference was -0.19 (95% CI -0.68 to 0.29) months. The difference in estimated benefits of treatment ranged from -7.0% to 7.2% for RR and -2.0 to +2.4 months for PFS; there was no evidence of systemic bias by INV (P = 0.54 for RR and 0.31 for PFS). CONCLUSION: INV overestimate RR compared with IRC. Given the variability in assessing RR and PFS between INV and IRC, an IRC should be considered if the primary end point is on the basis of assessments of changes in tumor lesions.

Correlation of changes between 2-year disease-free survival and 5-year overall survival in adjuvant breast cancer trials from 1966 to 2006.

BACKGROUND: Although disease-free survival (DFS) is accepted as a valid end point in adjuvant breast cancer trials, improvement in 2-year DFS has never been formally established as an adequate correlate for 5-year overall survival (OS). We set out to ascertain if changes in 2-year DFS can be used to accurately predict 5-year OS changes. DESIGN: We conducted a systematic Medline search (1966-2006) for randomized adjuvant breast cancer trials of >100 patients per arm with 2-year DFS and 5-year OS data. A univariate regression model weighted by trial sample size was constructed to determine whether 2-year DFS differences between treatment arms within trials were predictive of 5-year OS differences. RESULTS: A total of 126 studies containing 149 treatment comparisons met the inclusion criteria. Difference in 2-year DFS was a significant predictor of difference in 5-year OS. For every 1% increase in 2-year DFS difference, the 5-year OS difference increased by 0.5%-0.55%. The proportion of variation explained ranged from 0.38 to 0.42, with a wide prediction interval. CONCLUSION: There is a statistically significant correlation, of moderate strength, between difference in 2-year DFS between treatment comparisons and difference in 5-year OS but the correlation is not strong enough to be used as a predictor.

Role of AVP in mediating the altered core temperature response to a simulated open field in pregnant rats.

Near the term of pregnancy, rats have an attenuated core temperature response on exposure to a novel environment (e.g., a simulated open field) compared with that observed early in pregnancy or in nonpregnant rats. The present experiments were carried out on 26 nonpregnant and 26 pregnant rats to test the hypothesis that arginine vasopressin, functioning as an endogenous antipyretic substance in the central nervous system, mediates this attenuated core temperature response. Exposure to a simulated open field after intracerebroventricular (ICV) vehicle produced a significant increase in core temperature in both nonpregnant and pregnant animals, the magnitude and duration of which were greater in the nonpregnant rats. In nonpregnant rats, exposure to a simulated open field after ICV vasopressin V(1)-receptor antagonist altered the pattern of the core temperature response but not the core temperature index compared with that observed on exposure to a simulated open field after ICV vehicle. In pregnant animals, ICV vasopressin V(1)-receptor antagonist did not alter the core temperature response to a simulated open field compared with that observed after ICV vehicle. Thus our data do not support the hypothesis that a pregnancy-related activation of arginine vasopressin attenuates the core temperature response to a simulated open field in rats near the term of pregnancy.

Pregnancy alters body-core temperature response to a simulated open field in rats.

Exposure of a rat to a novel environment (e.g., a simulated open field) induces a transient increase in body-core temperature, which is often called stress-induced hyperthermia. Although pregnancy is known to influence thermoregulatory control, its effect on stress-induced hyperthermia is unknown. Therefore, 24 Sprague-Dawley rats (8 nonpregnant and 16 pregnant) were studied to test the hypothesis that pregnancy would alter the development of stress-induced hyperthermia after exposure to a simulated open field. Body-core temperature index increased significantly after exposure to a simulated open field in nonpregnant and gestation day-10 rats but not in gestation day-15 and day-20 rats. Thus our data provide evidence that pregnancy influences the body-core temperature response of rats exposed to a simulated open field in a gestation-dependent fashion. The functional consequences as well as the mechanisms involved remain to be determined.

Influence of nicotine on the core temperature response to a novel environment in pregnant rats.

Exposure of a male or nonpregnant female rat to a novel environment, such as a simulated open field, induces a transient increase in core temperature, which is often called stress-induced hyperthermia. Pregnancy alters this response such that the core temperature index increases significantly during exposure to a simulated open field on day 10 but not on days 15 and 20 of gestation in rats. The present experiments were carried to investigate the effect of chronic administration of nicotine (0, 1, 2, 4, or 8 mg.kg-1.24 h-1 for 13-15 days) on the core temperature response to a simulated open field in chronically instrumented pregnant (day 20 or 21 of gestation) and nonpregnant Sprague-Dawley rats. In nonpregnant rats, the core temperature index increased more during exposure to a simulated open field after chronic administration of nicotine at all doses than after chronic administration of vehicle; the core temperature response was not dependent on the dose of nicotine. In pregnant rats, significant increases in core temperature as well as in the core temperature index occurred only during exposure to a simulated open field after chronic administration of nicotine in doses of 2, 4, or 8 mg.kg-1.24 h-1; the core temperature response was dependent on the dose of nicotine. Our data provide evidence that chronic exposure to nicotine enhances the core temperature response to a simulated open field in nonpregnant rats and unmasks a maternal thermogenic response that is not seen to the same stimulus near term of pregnancy. The possible physiological consequences for the fetus are presently unknown and require investigation.