A step section method for full histopathological assessment of carcinogen-affected target tissue during respiratory carcinogenesis

Chronic nose-only inhalation study in rats, comparing room-aged sidestream cigarette smoke and diesel engine exhaust

Nose-only exposure of male and female Wistar rats to a surrogate for environmental tobacco smoke, termed room-aged sidestream smoke (RASS), to diesel engine exhaust (DEE), or to filtered, fresh air (sham) was performed 6 hours/day, 7 days/week for 2 years, followed by a 6-month post-exposure period. The particulate concentrations were 3 and 10 mg/m3. Markers of inflammation in bronchoalveolar lavage showed that DEE (but not RASS) produced a dose-related and persistent inflammatory response. Lung weights were increased markedly in the DEE (but not RASS) groups and did not decrease during the 6-month post-exposure period. Bulky lung DNA adducts increased in the RASS groups, but not in the DEE groups. Cell proliferation in the lungs was unaffected by either experimental treatment. Histopathological responses in the RASS groups were minimal and almost completely reversible; lung tumors were similar in number to those seen in the sham-exposed groups. Rats exposed to DEE showed a panoply of dose-related histopathological responses: largely irreversible and in some cases progressive. Malignant and multiple tumors were seen only in the DEE groups; after 30 months, the tumor incidence (predominantly bronchiolo-alveolar adenomas) was 2% in the sham-exposed groups, 5%in the high RASS groups, and 46% in the high DEE groups (sexes combined). Our results suggest that in rats exposed to DEE, but not to RASS, the following series of events occurs: particle deposition in lungs --> lung "overload" --> pulmonary inflammation --> tumorigenesis, without a significant modifying role of cell proliferation or DNA adduct formation.

Bronchial carcinogenesis in syngeneic hamsters

Endobronchial sustained release implants of carcinogen were placed in males (m) and females (f) of four varieties of syngeneic hamsters: BIOF1D; BIO87.20; BIO1.5; BIO15.16. The sequential progression of carcinogenesis that occurred was faster for 1.5m than for 1.5f (P = 0.01) and less rapid for 15.16m than for 87.20m and F1Dm (P < 0.05). Fewer invasive cancers occurred in 15.16m than in the other male varieties (P < 0.01), in 1.5m than in 87.20m (P < 0.05), and in 87.20f than in 87.20m (P < 0.05). Adenocarcinoma occurred with greater frequency in the 1.5 variety than in the F1D variety (P < 0.05). Significant variability in susceptibility, incidence, and types of invasive cancers formed exists, providing new opportunities for further study of bronchial carcinogenesis.

Histogenesis of adenosquamous bronchogenic carcinoma

In our hamster lung cancer model studies, among 463 non-small-cell lung cancers (NSCLC), there were 47 adenosquamous neoplasms. In 24 of 27 lesions with diameters of less than 3.0 mm, the adenocarcinoma and the squamous cell carcinoma components arose as separate, spatially discrete lesions, but these were separate in only 7 of 20 lesions with diameters of 30 mm or greater. Co-infiltration of the components became more frequent as tumor size increased. The usual adenosquamous variety of NSCLC is likely a collision tumor, with each component possessing separate biological characteristics. Thus, future prognostically directed studies of this variety of NSCLC must recognize that these neoplasms have two components, each of which needs to assessed.