QUANTITATION OF PREINVASIVE NEOPLASTIC PROGRESSION IN ANIMAL-MODELS OF CHEMICAL CARCINOGENESIS

An assay method that precisely quantitates the cellular and tissue cha nges associated with early, preinvasive neoplasia is much needed as a surrogate endpoint biomarker (SEB) in clinical trials to predict the p otential efficacy of chemopreventive agents in bringing about cancer i ncidence reduction. Quantification of histological changes at the tiss ue level are potentially powerful SEB's since these visually apparent changes are common in all neoplastic development, regardless of tissue type or neoplastic cause. Currently subjective inspection of the hist ological appearance of sectioned and stained material, or ''grading,'' by experienced pathologists is used to evaluate neoplastic progressio n. This has well-known limitations of reproducibility accuracy, and re solution of grading scale. Since neoplastic changes are visually appar ent and morphologic in nature, quantification by image analysis is a m easurement modality of choice. Image analysis was implemented through the use of high-resolution ''tiled'' images of complete tissue section s. A histological grading system, or ''scale,'' was developed that cou ld be expressed in terms of normal deviate units of multiple and diffe rent morphometric descriptors. Neoplastic growth was characterized qua ntitatively with multiple measurements on each tissue image tile, whic h were combined into a single number for each tile, i.e., a histologic grade per tile, and parameters from the distributions of these measur ements were used to represent the histologic grade for the entire regi on considered. This concept provided a uniform final scale in similar units of measurement, regardless of which tissues were graded. Also, t he grading scale automatically adjusted measurement variance for diffe rent tissues by using normal tissue for each different type to obtain the normalization to standard deviation it) units. This further define d a uniform final scale and maintained standard references. Using this method, results from two weil-known animal models of carcinogenesis, squamous cell carcinoma of SENCAR mouse skin induced by benzo(a)pyrene (B[a]P), and squamous cell carcinoma of the rat esophagus induced by N-nitrosomethylbenzylamine (NMBA), were compared to each other. Image analysis was performed on skin tissue sections from a total of 64 SENC AR mice, and esophagus tissue sections from 96 Fischer-344 rats. In bo th cases, a quantitative expression of the preinvasive neoplastic resp onse to the carcinogen as a function of time of exposure was expressed along a continuous grading scale in standard deviation units (z). in the SENCAR mouse skin animal model, similar cohorts of 4 mice at 20 we eks showed significant modulation of B[a]P-induced neoplasia by treatm ent with the antiproliferative agent difluoromethylornithine, P<.05. I n the rat esophagus animal model, similar cohorts of 6 rats at 10 and 15 weeks showed significant modulation of NMBA-induced neoplasia by tr eatment with the antimutagen phenethyl isothiocyanate, P<.05. (C) 1998 Wiley-Liss, Inc.