Libby amphibole exposure in rat models of cardiovascular disease seen in LA-exposed SHHF rats were classified as atypical based on the stacking of cells, but they were not classified as adenomatous. Such atypical lesions have been noted in broncho- alveolar neoplasia and atypical adenomatous hyperplasia of the lung in humans and have been associated with genetic changes in the epi- thelial growth factor (EGF) receptor (McIntire et al. 2010). EGF receptor expression as evi- denced from gene array analysis was up-regu- lated by LA exposure only in SHHF rats. Case studies with asbestos exposure have shown the coexistence of atypical adenomatous hyper- plasia, primary lung adenocarcinoma, and pleu- ral mesothelioma (Tsuzuki et al. 2008). Because these lesions seen in SHHF rats at 3 months did not progress over 6 months, ascertaining their significance is difficult. However, chronic exposure to LA may lead to the development of adenoma in SHHF rats. TP53 (tumor protein 53) is a key tumor suppressor gene that was induced only in WKY rats exposed to LA. The loss of function of TP53 has been implicated in the development of lung cancer and cellular proliferation after asbestos exposure (Morris et al. 2004). C-Fos (FOS; FBJ murine osteo- blastoma viral oncogene homolog)–induced growth factor, a member of the AP-1 oncogene family implicated in cell motility and invasion (Han et al. 2010), and the FBJ (murine osteo- sarcoma viral oncogene homolog) oncogene were up-regulated only in LA-exposed SHHF rats. The expression of EGF receptor impli- cated in hyperplastic cell growth (Adiseshaiah et al. 2008) was also increased in SHHF rats, as discussed previously. A number of cellular pro- cesses indicated significant changes in pathways in cancer and basal cell carcinoma development, especially in SHHF rats. This may facilitate the proliferative phenotype seen in the SHHF rats after LA exposure. Baseline high levels of oxida- tive stress and inflammation in SHHF rats may also increase their sensitivity to develop prolif- erative lesions. Thus, the SHHF rat may be an appropriate model to study early predisposition to proliferative changes after asbestos exposure in humans. Certain limitations of the study should be considered in the interpretation of these find- ings. First, in addition to Fe overload, the base- line CVD of the SH and SHHF rats may play a role in susceptibility to LA. Second, the use of intratracheal instillation, although allowing pre- cise control for pulmonary dose, might produce a one-time bolus response relative to inhalation that may overwhelm normal repair mechanisms. Third, the temporality of gene expression pat- terns was not considered, and analysis of whole- lung tissue expression may dilute changes seen at the site of lesion. Follow-up studies using the SHHF rat as a model of pulmonary hyperplasia could be done with microdissection of lesions to analyze unique changes in gene expression of these hyperplastic cells. Finally, because LA has a shorter overall fiber length distribution than other well-studied fibers, the kinetics of retention and effects on pulmonary cells may be different. LA was chosen for this study because of its human relevance; however, future studies are needed to assess the effects of longer fibers in the SHHF rat. Conclusion We report that preexisting host Fe overload, as in the case of CVD, results in progressive accumulation of Fe over time within fiber- laden alveolar macrophages in rats exposed to LA. This accumulation of Fe is not associated with increased LA-induced inflammatory gene expression or fibrosis. Moreover, LA-exposure in SHHF rats is associated with the development of atypical hyperplastic lung lesions of bron- chiolar origin. 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