The advancement of an investigational new drug in humans is a significant developmental milestone. In first-in-human (FIH)-enabling toxicology studies, the highest dose without a test article–related adverse effect (no-observed-adverse-effect-level [NOAEL]) serves as the basis for deriving a safe FIH starting dose. For anticancer pharmaceuticals, the FIH dose may be calculated using the highest non-severely toxic dose (HNSTD) in nonrodent models or the dose severely toxic to 10% (STD10) in rodents. Given the practice of reporting the NOAEL, but the lack of regulatory requirements to do so for anticancer pharmaceuticals, we conducted an informal survey of 20 companies to answer the question “How is our industry reporting toxic/adverse dose levels in FIH-enabling toxicology studies for anticancer indications?” The data indicated 4 reporting approaches, each providing a path to regulatory acceptance. Within the integrated toxicology study report, 45% of respondents report the HNSTD/STD10, 25% report the NOAEL, 20% report both the HNSTD/STD10 and NOAEL, and 10% do not define either, reserving definitions for regulatory submissions. One reporting approach may be preferred over another for reasons including consistency across indications, repurposing pharmaceuticals, regulatory feedback, or simplicity. The reporting approach should be defined in advance of study initiation, and the pathologist should provide context to support the chosen approach.

Idiopathic femoral head chondrolysis is a recognized condition in human adolescents and has previously been reported in two macaques at a biomedical research facility. A cluster of coxofemoral joint abnormalities consistent with this condition affecting seven cynomolgus macaques over a four-month period in 2016 and 2017 was observed at a single, nonclinical contract research facility, prompting enhanced physical examination screening efforts during animal receipt and pre-study evaluation to identify additional affected animals. This article summarizes the results of this investigation from November 2016 to March 2021, yielding 97 total cases for an overall incidence of 0.54% (97/17,898 macaques). Affected animals were presented with one or more of the following unilateral or bilateral findings on physical examination and/or diagnostic imaging: lameness, palpable coxofemoral joint abnormalities, femoral head atrophy with variable loss of articular cartilage and irregularity of the femoral head surface, enlarged joint space with effusion, and increased radiographic density of the femoral head. This condition prevented use of affected animals on study for 54% of the cases (52/97 animals). Recognition of this idiopathic condition is important in drug safety evaluation studies to distinguish it from test article–related effects.

Aneurysms of the ascending aorta, unrelated to xenobiotic administration, are described in 5 rats and 2 mice in nonclinical safety studies conducted at Charles River Laboratories (CRL) sites over the past 10 years. The most prominent microscopic finding was focal dilation with disruption of the wall of the ascending aorta with chronic adventitial inflammation or fibroplasia. The pathogenesis of this finding is unknown. There were no associated macroscopic findings, clinical abnormalities, or vascular lesions elsewhere. The results of a search of historical control data from toxicology studies of 1 day to 72 weeks' duration performed at CRL for aortic findings from 5900 mice and 23,662 rats are also reported. Aortic lesions are uncommon in mice and rats used in nonclinical safety studies, but toxicologic pathologists should be aware that aneurysms of the ascending aorta with fibroplasia and inflammation in the aortic wall and adventitia may occur spontaneously or iatrogenically, as they have the potential to impact interpretation in toxicology studies.

Cynomolgus macaques, the most commonly utilized nonhuman primate in nonclinical toxicology studies, are acquired from purpose-bred colonies across various geographic locations, including China, Cambodia, and Vietnam. Importation challenges and limited availability have restricted animals suitable for inclusion in nonclinical studies. The coronavirus disease 2019 (COVID-19) outbreak further stressed supply chains, reducing the ability to source animals from a singular location to complete a drug development program. These challenges raised concerns of increased variability in study endpoints due to heterogeneity of animals and that this could subsequently impact historical control data and toxicology study interpretation. To investigate the impact of Chinese, Vietnamese, or Cambodian geographic origin on standard nonclinical toxicology study endpoints, historical control data from studies conducted at a single facility from 2005 to 2020 were compiled and evaluated for the following: clinical observations, body weight, ophthalmoscopic examinations, and clinical and anatomic pathology data. Study populations consisted of 2- to 5-year-old cynomolgus macaques sourced from China (n = 750 males/741 females), Cambodia (n = 282 males/271 females), and Vietnam (n = 122 males/120 females). Interpretation of the various data demonstrated no notable differences in standard toxicology study endpoints or background findings among cynomolgus macaques originating from China, Cambodia, or Vietnam.

Nonclinical rodent studies with repeat slow intravenous dosing, such as safety assessments of anticancer therapeutics, often require the use of animals with surgically implanted catheters. Catheterization is a relatively short surgical procedure but requires use of anesthesia. Ketamine/xylazine injectable anesthesia is typically used because it has advantages over inhalation anesthesia including ease of administration, safety and predictability of effects, and relatively low cost. However, ketamine/xylazine anesthesia in rodents can also be associated with the development of undesirable corneal lesions of uncertain mechanism such as mineralization of Bowman's membrane or stroma, erosion/ulceration, inflammation, fibroplasia, and neovascularization. Such findings have the potential to confound study interpretation in programs for which the cornea is a potential target tissue. This case report describes the occurrence of ketamine/xylazine-related corneal lesions observed in surgically catheterized rats in a 16-day toxicity study for an oncology compound.

The Society of Toxicologic Pathology (STP, https://www.toxpath.org/) was founded in North America in 1971 as a nonprofit scientific and educational association to promote the professional practice of pathology as applied to pharmaceutical and environmental safety assessment. In the ensuing 50 years, the STP has become a principal global leader in the field. Society membership has expanded to include toxicologic pathologists and allied scientists (eg, toxicologists, regulatory reviewers) from many nations. In addition to serving membership needs for professional development and networking, major STP outreach activities include production of articles and presentations designed to optimize toxicologic pathology procedures ("best practice" recommendations), communicate core principles of pathology evaluation and interpretation ("points to consider" and "opinion" pieces), and participation in international efforts to harmonize diagnostic nomenclature. The STP has evolved into an essential resource for academic, government, and industrial organizations that employ and educate toxicologic pathologists as well as use toxicologic pathology data across a range of applications from assessing product safety (therapies, foods, etc) to monitoring and maintaining environmental and occupational health. This article recapitulates the important milestones and accomplishments of the STP during its first 50 years.

Detection of test article–related effects and the determination of the adversity of those changes are the primary goals of nonclinical safety assessment studies for drugs and chemicals in development. During these studies, variables that are not of primary interest to investigators may change and influence data interpretation. These variables, often referred to as “nuisance factors,” may influence other groups of data and result in “block or batch effects” that complicate data interpretation. Definitions of the terms “nuisance factors,” “block effects,” and “batch effects,” as they apply to nonclinical safety assessment studies, are reviewed. Multiple case examples of block and batch effects in safety assessment studies are provided, and the challenges these bring to pathology data interpretation are discussed. Methods to mitigate the occurrence of block and batch effects in safety assessment studies, including statistical blocking and utilization of study designs that minimize potential confounding variables, incorporation of adequate randomization, and use of an appropriate number of animals or repeated measurement of specific parameters for increased precision, are reviewed. [Box: see text]

Supplemental Material, sj-docx-1-tpx-10.1177_0192623320906385 for Scientific Regulatory Policy Committee Points to Consider*: Nuisance Factors, Block Effects, and Batch Effects in Nonclinical Safety Assessment Studies by Albert Eric Schultze, Bindu Bennet, Jessica Caverly Rae, Alan Y. Chiang, Kendall Frazier, Paula Katavolos, LuAnn McKinney, Daniel J. Patrick and Niraj Tripathi in Toxicologic Pathology

In the article "Opinion on Designation of Adverse and Nonadverse Histopathological Findings in Toxicity Studies: The Pathologist's Dilemma," the authors Gopinath and Mowat provide a framework for designation of adversity supplemented with photomicrographic examples. Given that adversity designation can significantly impact the no observed adverse effect level and clinical trial design, it is important to carefully consider all of the criteria by which such assignments are made. We highlight some of the specific assertions within the article that could benefit from a more detailed discussion. Our primary criticism surrounds the authors' primary reliance on histopathology in isolation for adversity designation, which in our opinion provides an overly simplified depiction of the process. We provide additional perspective on how context beyond histopathology often plays a critical role in adversity designation and highlight areas where inclusion of some of these scenarios would have provided the reader a more realistic view of the complex process of assigning adversity. * This is an opinion article submitted to the Toxicologic Pathology Forum. It represents the views of the authors. It does not constitute an official position of the Society of Toxicologic Pathology, British Society of Toxicological Pathology, or European Society of Toxicologic Pathology, and the views expressed might not reflect the best practices recommended by these Societies. This article should not be construed to represent the policies, positions, or opinions of their respective organizations, employers, or regulatory agencies.

The severity grade is an important component of a histopathologic diagnosis in a nonclinical toxicity study that helps distinguish treatment-related effects from background findings and aids in determining adverse dose levels during hazard characterization. Severity grades should be assigned based only on the extent (i.e., amount and complexity) of the morphologic change in the examined tissue section(s) and be clearly defined in the pathology report for critical lesions impacting study interpretation. However, the level of detail provided and criteria by which severity grades are assigned can vary, which can lead to inappropriate comparisons and confusion when evaluating pathology results. To help address this issue, a Working Group of the Society of Toxicologic Pathology’s Scientific and Regulatory Policy Committee was formed to provide a “points to consider” article on the assignment and application of pathology severity grades. Overall, the Working Group supports greater transparency and consistency in the reporting of grading scales and provides recommendations to improve selection of diagnoses requiring more detailed severity criteria. This information should enhance the overall understanding by toxicologic pathologists, toxicologists, and regulatory reviewers of pathology findings and thereby improve effective communication in regulatory submissions.

Development of new biomedical products necessitates nonclinical safety assessment in animals as a means of assessing potential risk to human patients. Pivotal nonclinical safety studies that support human clinical trials are performed according to Good Laboratory Practice (GLP) guidelines, which are designed to ensure that the study was conducted under carefully controlled conditions using standardized and validated procedures that will yield a reliable, reproducible, and traceable data set. The GLP guidelines established by different regulatory agencies address organizational structure, personnel responsibilities, personnel training practices, quality assurance (ensuring compliance), facilities, equipment, standard operating procedures, study documentation (record keeping), and record and sample retention. Academic institutions engaging in nonclinical safety assessment on-site have multiple options for implementing a GLP quality system. This article outlines the rationale supporting the use of a GLP-compliant or GLP-like quality system in academia and reviews key concepts needed to efficiently and effectively implement GLP in the academic setting. Emphasis is given to provision of GLP-compliant pathology support as (1) pathology data are an essential component of GLP nonclinical safety testing, (2) familiarity with pathology-related GLP procedures typically is gained first outside the academic setting, and (3) microscopic pathology diagnoses and interpretations require special accommodations to ensure that they are undertaken in a GLP-compliant fashion.

This article presents the historical control data of spontaneous tumors in Tg.rasH2 published in 2013 (2004-2012) and compares and contrasts it to more recent data collected from 2013 to 2018, reporting differences in the average percentage incidences or incidence ranges as well as the incidence of new tumors. In 2013, we published a comprehensive review of spontaneous tumors in Tg.rasH2 mice used in 26-week carcinogenicity studies, which included data from control dose groups from 26 studies and a total of 710 mice per sex. The total database, now including the more recent data, has nearly doubled the number of animals, completing to date a total of 52 studies in males and 51 studies in females for a total of 1,615 male mice and 1,560 female mice, respectively. In this article, we compare the data collected from 2004 to 2012 against the data collected from 2013 to 2018 and the overall tumor incidence change.

In 2014, the Organisation for Economic Co-operation and Development (OECD) issued guidance no. 16, Guidance on the GLP Requirements for Peer Review of Histopathology. The stated purpose of the guidance document is "to provide guidance to pathologists, test facility management, study directors and quality assurance personnel on how the peer review of histopathology should be planned, managed, documented, and reported in order to meet Good Laboratory Practice (GLP) expectations and requirements." On behalf of and in collaboration with the global societies of toxicologic pathology, the Society of Toxicologic Pathology initiated a review of OECD guidance no. 16. The objectives of this review are to provide a unified interpretation of the guidance, to recommend compliant processes for organizations to implement, and to avoid inconsistent process adaptations across the industry. This review of the guidance document is the product of a global collaboration with other societies of toxicologic pathology and provides a section-by-section international consensus view and interpretation of the OECD guidance on peer review.

Toxicologic pathology plays a critical role in the safety assessment of nonhuman primates used in drug development through the identification and interpretation of microscopic tissue changes. The discrimination between background changes, or those changes that are incidental/spontaneous, and true test article-related findings is of paramount importance and can be challenging. The practice of toxicologic pathology is both an art and a science, and the accurate identification and interpretation of histopathologic changes relies on the experience of the pathologist as well as utilization of as much applicable information as possible. This includes study design, organ weights, treatment, and historical control data as well as the use of proper terminology, thresholds, and quality control. Also intrinsic to this process is having a solid understanding of the common background microscopic changes in nonhuman primates that are commonly used in nonclinical research.

Nonhuman primates (NHPs) are valuable research candidates because of their anatomic, physiologic, and immunologic similarities to humans. Macaques in particular play a vital role in a wide range of studies ranging from preclinical pharmaceutical development to animal model research. There are established standard core tests for hematology, coagulation, clinical chemistry, and urinalysis in NHPs used in biomedical research studies. These tests can provide key information on organ function/injury, pathophysiologic mechanisms, and overall health of the animal. Additional parameters are often added to the core tests to elucidate additional information based on the type and duration of the study (e.g., subacute and subchronic), type of compound being tested, and/or anticipated pathologic effects. A brief overview of some of the more common spontaneous microscopic changes (background lesions) in NHPs is also provided, some of which have the potential to impact clinical pathology endpoints and study interpretation. It is important to have knowledge of both clinical and anatomic pathology findings, including the relevance of background lesions, before making firm conclusions regarding specific pathologic findings.