Immunohistochemical and immunoradiometric evaluations of total cathepsin D in human larynx

By using a commercially available immunoradiometric technique (Cath-D-IRMA, Cis BioInt.) the distribution of total cathepsin D (cath-D) in 30 malignant and in the corresponding histologically-proven non-malignant fragments obtained from lymph node negative patients suffering from larynx cancer was investigated. In both tissues the oestrogen and progesterone receptors were also assayed. In 17 out of the 30 samples, the cath-D was also assayed by immunohistochemistry using the M1G8, a mouse monoclonal antibody raised against cath-D (Cis BioInt.). Our data indicate that cath-D is present in prismatic cells of the normal laryngeal epithelium and in the cancerous cells. In cancerous larynx, the outer cell layer of large tumour nests showed the highest degree of immunoreactivity, while fibroblasts and inflammatory cells always showed a very faint staining. Cathepsin D levels were significantly higher (P < 0.0001) in the cancerous fragments (with a mean of 33 +/- 3.4 pmol/mg protein) than in the corresponding non-cancerous specimen (with a mean of 20.8 +/- 2 pmol/mg protein). A significant positive association (P < 0.001) between cath-D and progesterone receptor (PR) concentration values in the cancerous larynx was observed; accordingly, tumours expressing PR had significantly (P = 0.0005) higher cath-D levels than the tumours which did not contain the receptor. In contrast, such a relationship was absent in the non-malignant specimens. As regard the oestrogen receptor, no significant relationship between this and cath-D was observed. We conclude that cath-D measured by IRMA in tissue cytosols is mainly derived from cancerous cells, the contribution from fibroblasts and inflammatory cells being negligible. Cathepsin D overexpression and association with the PR in the malignant part of the larynx could indicate a possible role of the receptor in the biology of this disease.