All materials reviewed during the PWG were provided by the sponsoring companies. For studies conducted in mice and hamsters in which proliferative vascular changes were of interest, 2 unstained slides were submitted to EPL. Six unstained slides were submitted from studies conducted in rats, since it was anticipated that either special histochemical or immunohistochemical stains might be helpful in the diagnosis. There were a total of 420 cases submitted from studies conducted in mice, 10 cases submitted from hamsters, and 99 cases submitted from rats.
It was critical that the origin of the slides being reviewed by the PWG be kept confidential. Individuals involved in organizing and conducting the PWG and the panel members did not know the company, study, or compound for any of the slides being reviewed. In order to achieve this degree of confidentiality, EPL provided glassware to be used to submit the unstained tissue sections. All glass slides were purchased from the same vendor and were the same style and color. The slides had preprinted numbers. The slides were initially numbered consecutively, and then were arranged in a random order according to a computer-generated list of random numbers.
The randomized slides were submitted to HESI for distribution to the participating companies. Upon request, the number of slides requested was sent by HESI to each of the companies making submissions. The slides were labeled with only the random number. No other information appeared on the glass slide. When submitting the material, the company also submitted a log containing the random number, animal number, species, tissue of origin, and indicated if it was a control or treated animal and if it was sacrificed or died spontaneously. If the animal died or was euthanized prior to the scheduled sacrifice, the log also included the weeks on study or the number of weeks on treatment and the probable cause of death if available. All slides were first submitted to HESI from the companies participating in the project. As submissions were received by HESI, the slides and the complete log were repackaged and shipped to EPL to be used for the PWG without any accompanying information concerning the origin of the slides.
When received at EPL, the randomized slides were rearranged in the original numerical order. All studies were combined, thus precluding the association of a particular slide with a particular study. Since all the slides with random numbers were not used for the PWG, the slides used for the PWG were assigned ascending consecutive identification numbers (ID#). This provided a third level of coding of the slides (triple blind) and made the review of the slides by the PWG easier since they only had to be concerned about a single consecutive number when recording their findings. This approach ensured the complete confidentiality of the materials being submitted.
EPL stained one slide from each case submitted with hematoxylin and eosin (H&E). The remaining slides were available for diagnostic histochemical or immunohistochemical staining that might help in the definitive classification of selected lesions. Prior to convening the PWG, the Chairperson reviewed all cases submitted and requested representative special stains that could be used in addition to the routine H&E stained slides. The histochemical stains which were used included: Masson’s trichrome, alcian blue/periodic acid Schiff (PAS), and Mallory’s phosphotungstic acid hematoxylin (PTAH). Immunohistochemical stains that were applied to selected cases included: S-100 (liposarcoma), Desmin (muscle differentiation), and Uncoupling Protein-1 (UCP-1) (Hibernoma).
The Pathology Working Group (PWG) meeting, consisting of independent consulting pathologists with expertise in toxicologic pathology, with specific emphasis on rodent carcinogenicity studies, was held in Herndon, Virginia, January 16-18, 2007. The purpose of the PWG was to develop a consensus for tumor diagnoses and consistency of diagnoses across multiple studies for hemangiosarcomas in mice or hamsters and liposarcomas/fibrosarcomas in rats. The focus of the PWG review was to establish consistent tumor diagnostic criteria, assess evidence of preneoplastic changes, and evaluate morphologic differences between spontaneous changes examined from controls with similar changes from treated animals.
The PWG Chairperson (JFH) organized the meeting and was responsible for conducting the meeting, leading the discussion, and preparing a report of the PWG’s findings. The PWG participants included board-certified medical (PG) and veterinary pathologists (MRE, HE, DEM, PCM, and PAT). Several interested scientists from the HESI PPAR Agonist Project Committee or from sponsoring member companies were also in attendance as observers. At the beginning of the PWG meeting, the PWG Chairperson provided the panel with a review of the issues to be addressed and an outline of the approach to be followed. The PWG examined coded slides without knowledge of the specific test article or the origin of the case selected for their review.
The PWG examined H&E stained slides from all rats (99 cases) for which lesions were submitted. If the diagnosis using only the H&E stained sections was uncertain, selected histochemical and immunohistochemical stains were available for some cases for PWG review to aid in classification of tumors. Due to the large number of cases submitted for the mouse portion of the PWG, the PWG Chairperson selected representative cases to include the entire spectrum of non-neoplastic changes and benign and malignant neoplasms available from the slides submitted. Since there were only 10 cases submitted from the hamster study, the PWG examined all slides from hamsters. No histochemically or immunohistochemically stained slides were prepared for the examination of vascular lesions in mice or hamsters.
Each participant recorded their diagnoses and comments on worksheets which were prepared by the PWG Chairperson. The PWG participants recorded either a morphologic diagnosis of a proliferative change or made an observation of “no proliferative lesion,” if no significant hyperplastic or neoplastic changes were identified. The diagnosis for each case examined was discussed by the group, reexamined if necessary, and the final opinion was recorded by the Chairperson.
During the review, the PWG participants developed recommended nomenclature and diagnostic criteria for each of the changes discussed. Following the PWG, an illustrated lexicon was prepared in the form of an interactive CD-ROM which included the nomenclature and diagnostic criteria recommended by the Pathology Working Group and representative photomicrographs of each of the changes including both non-neoplastic proliferative lesions and neoplasms and also a list of important references related to the project. A copy of this illustrated lexicon is present in the back cover of this issue of the journal.