Recommendations for the interpretation of renal tubule proliferative lesions occurring in rat kidneys with advanced chronic progressive nephropathy (CPN).

There is little guidance in the literature on the spectrum of proliferative tubule lesions in the kidneys of aging rats affected with spontaneously occurring, chronic progressive nephropathy (CPN), or their interpretation. Through accessing 2-year carcinogenicity studies in male F344 rats held in the Archives of the National Toxicology Program, NIEHS, a large number of cases of advanced CPN have been surveyed histopathologically for proliferative tubule lesions, and an attempt made to provide guidelines for discrimination of lesions common to the CPN process, from those representing precursors of neoplasia. Several proliferative lesions were identified as common in advanced CPN with no apparent evidence supporting a role in renal tubule carcinogenesis. It is recommended that these lesions be viewed generically as CPN tubule profiles, and not recorded separately from the diagnosis of CPN. Criteria were developed to distinguish these CPN-associated lesions from atypical tubule hyperplasia, a precursor of adenoma, both of which were also represented in this survey of advanced CPN.