Propagation of a poorly differentiated human pulmonary adenocarcinoma in nude athymic rats

Nude athymic rats of Rowett genetic background were injected subcutaneously with cells from a poorly differentiated human pulmonary adenocarcinoma, following propagation in nude mice. The tumour cells were obtained by thoracentesis and by pleural biopsy during thoracoscopy. So far, we have heterotransplanted 13 different malignant human tumours including malignant mesothelioma, pulmonary adenocarcinoma, malignant melanoma and malignant lymphoma. Subcutaneous tumour growth was seen in all inoculated animals, with an exponential tumour growth pattern and with tumour volume doubling times of approximately 8 days. After two initial passages in nude athymic mice of BALB/c genetic background, the human tumour so far has undergone 9 passages in athymic rats, i.e. collection of tumour material by biopsy from the preceding tumour-bearing rat generation, processing and inoculation of tumour brei with subsequent tumour growth have been repeated 8 times. Four-to-8-week-old rats of both sexes were used throughout and tumour growth was controlled by palpation twice a week. Routine histopathological sections were prepared from the tumour at various passages to assess similarity to the original tumour in the patient. The growth pattern of the xenografts remained similar at all passages just as the remarkable similarity of the heterotransplanted tumours to the original adenocarcinoma was retained at all passages. No spontaneous regressions of heterotransplanted tumours could be demonstrated. Electron microscopical analysis revealed numerous blunt microvilli and lumina partly filled with conglomerates of mucigen granules and small glycocalyceal bodies associated with external superficial microvilli. Scantiness of dark secretory granules together with free and membrane-bound polyribosomes were seen in the cytoplasm. We believe that the nude athymic rat is a valuable research tool and that the permanently transplantable human tumour reported here could be of value in delineating further the mechanisms for tumour take, growth and control.