Growth pattern of experimental squamous cell carcinoma in rat submandibular glands--an immunohistochemical evaluation

Histopathological and immunohistochemical studies during carcinogenesis in rat submandibular glands (SMGs) using a carcinogen (9,10-dimethyl-1,2-benzanthracene: DMBA) were evaluated. For carcinogenesis, the carcinogen-containing sponge was surgically inserted into the gland. Histopathological features during carcinogenesis were as follows; dilatation of ductal segments, the presence of duct-like structures and cystic lesion around the sponge were observed within 3 weeks of the experiment, squamous metaplasia in duct-like structures and lining epithelium of the cystic structures around the sponge were observed at 4-6 weeks of the experiment, and finally well differentiated squamous cell carcinomas (SCCs) were observed after 8 weeks of the experiment. The immunoreactivity of K8.12 keration (K8.12), S-100 protein (S-100), epidermal growth factor (EGF), laminin, and proliferating cell nuclear antigen (PCNA) were evaluated. In the normal SMG, EGF was confined to the granular cells and S-100 to the pillar cells of granular convoluted tubules (GCTs). K8.12 was found in striated (SD) and excretory duct (ED) cells and laminin showed linear staining of the basement membrane around the ducts, acini and blood vessels. PCNA-positive nuclei were rarely observed in the normal glandular parenchyma. During carcinogenesis, during the first stage, EGF in granular cells and S-100 in pillar cells of GCT segments disappeared, and cytokeration K8.12 was observed in duct-like structures and cystic epithelium around the DMBA sponge. PCNA-positive nuclei in the first stage were mainly confined to basal cells of morphologically altered ducts. During the second stage, squamous metaplastic cells showed an intense K8.12 reaction. During the third stage, the well differentiated SCC showed strong reaction for K8.12, and the linear staining for laminin staining had disappeared at the invading fronts. The PCNA index was nearly 40% in the tumour cell component. The stem cells or the progenitor cells during experimental carcinoma were most likely to be the ductal basal cells, and carcinogenesis was initiated with an increase of proliferating activity in small cell clusters surrounding a necrotic area, basal cells of dilated excretory ducts and duct-like structures. Thus, all ductal segments undergoing squamous metaplasia may participate in the genesis of neoplasia during experimental carcinogenesis.