Why the Atlas is Important

Purpose of the NTP Atlas of Nonneoplastic Lesions in Rats and Mice

Identifying potential human carcinogens in rodent bioassays has been a major focus of the testing strategy of the National Toxicology Program (NTP) for decades. However, nonneoplastic diseases are also a major cause of morbidity and mortality in humans, and many of these are thought to have environmental causes. The NTP Nonneoplastic Lesion Atlas (NNLA) provides diagnostic guidelines for microscopic nonneoplastic lesions in rats and mice in order to improve the understanding of nonneoplastic lesions and their relevance to human environmental diseases.

It can be challenging to make diagnoses that adequately capture all the tissue changes that are of a unique quality without generating an overwhelming amount of data. Accomplishing this in a manner that can be applied consistently and uniformly by a variety of pathologists requires acceptance of a certain degree of flexibility. The overall goal of this atlas is to improve the organization and diagnostic consistency of the NTP database. This will facilitate comparisons between studies, database searches, and generation of historical control data for nonneoplastic lesions. The atlas is intended for NTP staff and contract pathologists, but may be useful to other pathologists and scientists, or for training future pathologists.

An effort was made to maintain consistency with the nonneoplastic lesion terminology in the available International Harmonization of Nomenclature and Diagnostic Criteria (INHAND) monograph series and with the classification systems in the publications by Boorman et al. Pathology of the Fischer Rat: Reference and Atlas (1990) and Maronpot et al. Pathology of the Mouse: Reference and Atlas (1999). To maintain consistency with the NTP’s historical database, some atlas recommendations differ from the INHAND terminology.

The NNLA is intended as a dynamic document, which will be updated periodically to reflect evolving scientific consensus on appropriate diagnoses of nonneoplastic lesions in rats and mice.


Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds. 1990. Pathology of the Fischer Rat: Reference and Atlas. Academic Press, San Diego. Abstract:

Maronpot RR, Boorman GA, Gaul BW, eds. 1999. Pathology of the Mouse: Reference and Atlas. Cache River Press, Vienna, IL. Abstract: