Regulatory Forum.

Revision of the International Council for Harmonization (ICH) S1 guidance for rat carcinogenicity studies to be more selective of compounds requiring a 2-year rat carcinogenicity study has been proposed following extensive evaluation of rat carcinogenicity and chronic toxicity studies by industry and drug regulatory authorities. To inform the ICH S1 expert working group in their potential revision of ICH S1, a prospective evaluation study was initiated in 2013, in which sponsors would assess the pharmacologic and toxicologic findings present in the chronic toxicity studies and predict a positive or negative carcinogenicity outcome using a weight of evidence argument (a carcinogenicity assessment document [CAD]). The Scientific and Regulatory Policy Committee was asked by the Society of Toxicology Pathology (STP) executive committee to track these changes with ICH S1 and inform the STP membership of status changes. This commentary is intended to provide a brief summary of recent changes to the CAD guidance and highlight the importance of STP membership participation in the process of CAD submissions.

Regulatory Forum Opinion Piece*: Retrospective Evaluation of Doses in the 26-week Tg.rasH2 Mice Carcinogenicity Studies: Recommendation to Eliminate High Doses at Maximum Tolerated Dose in Future Studies. A Response to the Counterpoints.

We recently conducted a retrospective analysis of data collected from 29 Tg.rasH2 carcinogenicity studies conducted at our facility to determine how successful was the strategy of choosing the high dose of the 26-week studies based on an estimated maximum tolerated dose (MTD). As a result of our publication, 2 counterviews were expressed. Both counterviews illustrate very valid points in their interpretation of our data. In this article, we would like to highlight clarifications based on several points and issues they have raised in their papers, namely, the dose-level selection, determining if MTD was exceeded in 26-week studies, and a discussion on the number of dose groups to be used in the studies.

Regulatory Forum Opinion Piece*: Retrospective Evaluation of Doses in the 26-week Tg.rasH2 Mice Carcinogenicity Studies: Recommendation to Eliminate High Doses at Maximum Tolerated Dose (MTD) in Future Studies.

High doses in Tg.rasH2 carcinogenicity studies are usually set at the maximum tolerated dose (MTD), although this dose selection strategy has not been critically evaluated. We analyzed the body weight gains (BWGs), mortality, and tumor response in control and treated groups of 29 Tg.rasH2 studies conducted at BioReliance. Based on our analysis, it is evident that the MTD was exceeded at the high and/or mid-doses in several studies. The incidence of tumors in high doses was lower when compared to the low and mid-doses of both sexes. Thus, we recommend that the high dose in male mice should not exceed one-half of the estimated MTD (EMTD), as it is currently chosen, and the next dose should be one-fourth of the EMTD. Because females were less sensitive to decrements in BWG, the high dose in female mice should not exceed two-third of EMTD and the next dose group should be one-third of EMTD. If needed, a third dose group should be set at one-eighth EMTD in males and one-sixth EMTD in females. In addition, for compounds that do not show toxicity in the range finding studies, a limit dose should be applied for the 26-week carcinogenicity studies.

Regulatory Forum commentary: alternative mouse models for future cancer risk assessment.

International regulatory and pharmaceutical industry scientists are discussing revision of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) S1 guidance on rodent carcinogenicity assessment of small molecule pharmaceuticals. A weight-of-evidence approach is proposed to determine the need for rodent carcinogenicity studies. For compounds with high human cancer risk, the product may be labeled appropriately without conducting rodent carcinogenicity studies. For compounds with minimal cancer risk, only a 6-month transgenic mouse study (rasH2 mouse or p53+/- mouse) or a 2-year mouse study would be needed. If rodent carcinogenicity testing may add significant value to cancer risk assessment, a 2-year rat study and either a 6-month transgenic mouse or a 2-year mouse study is appropriate. In many cases, therefore, one rodent carcinogenicity study could be sufficient. The rasH2 model predicts neoplastic findings relevant to human cancer risk assessment as well as 2-year rodent models, produces fewer irrelevant neoplastic outcomes, and often will be preferable to a 2-year rodent study. Before revising ICH S1 guidance, a prospective evaluation will be conducted to test the proposed weight-of-evidence approach. This evaluation offers an opportunity for a secondary analysis comparing the value of alternative mouse models and 2-year rodent studies in the proposed ICH S1 weight-of-evidence approach for human cancer risk assessment.

Screening pharmaceuticals for possible carcinogenic effects: initial positive results for drugs not previously screened.

OBJECTIVE: To screen commonly used prescription drugs for possible carcinogenic effects. METHODS: In a large health care program we identified 105 commonly used drugs, not previously screened. Recipients were followed for up to 12½ years for incident cancer. Nested case-control analyses of 55 cancer sites and all combined included up to ten matched controls per case, with lag of at least 2 years between drug dispensing and cancer. Positive associations entailed a relative risk of 1.50, with p ≤ 0.01 and higher risk for three or more, than for one prescription. Evaluation included further analyses, searches of the literature, and clinical judgment. RESULTS: There were 101 associations of interest for 61 drugs. Sixty-six associations were judged to have involved substantial confounding. We found evidence that of the remaining 35, the following associations may not be due to chance: sulindac with gallbladder cancer and leukemia, hyoscyamine with nonHodgkin lymphoma, nortriptyline with esophageal and hepatic cancer, oxazepam with lung cancer, both fluoxetine and paroxetine with testicular cancer, hydrochlorothiazide with renal and lip cancer, and nifedipine with lip cancer. CONCLUSIONS: These preliminary findings suggest that further studies are indicated regarding sulindac, hyoscyamine, nortriptyline, oxazepam, fluoxetine, paroxetine, hydrochlorothiazide, and nifedipine.

International Conference on Harmonisation: guidance on testing for carcinogenicity of pharmaceuticals. Notice. Food and Drug Administration, HHS.

The Food and Drug Administration (FDA) is publishing a guidance entitled "S1B Testing for Carcinogenicity of Pharmaceuticals." The guidance was prepared under the auspices of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH). The guidance outlines experimental approaches to evaluating the carcinogenic potential of pharmaceuticals to humans that may obviate the necessity for the routine conduct of two long-term rodent carcinogenicity studies