Lumbar spine densitometry.

failure of antigen production is more likely to be due to genetic change associated with incomplete penetrance than to genetic loss. An alternative or additional possibility cannot, however, be excluded-that exuberant cell division causes dilution of a particulate cytoplasmic factor responsible for the formation of the antigen. Loss of organ-specific antigens could influence tumour metastasis by diminishing normal cell adhesion at the primary tumour site or by removing specific cell differences which might prevent secondary growth of tumour cells in another organ. A preliminary study has been made of the possible importance of the gastro-intestinal-specific antigen in this connexion: it could, in theory, behave as a " marker " antigen by coating the mucosal cell surface. However, the information so far available is too meagre for any useful discussion, though the absence of antigen in lymph-node metastases of all ten cases examined is a clear indication for further study. More investigation is also required to assess the possible diagnostic usefulness of immunofluorescence staining of gastro-intestinal tumours, especially for distinguishing between benign and premalignant polyps. Long-term follow-up studies of a large series of cases will be needed to confirm that the observed qualitative staining differences provide a reliable means of distinguishing benign from malignant states. Summary A gastro-intestinal-specific antigen demonstrated in mucoid cells by immunofluorescence staining and serological methods, probably an acid mucopoly-saccharide, was totally absent from 45 out of 54 gastro-intestinal carcinomas. In the remaining nine carcinomas, five of which were mucoid, staining of antigen was obtained in a small proportion of cells scattered among unstained acini. The immuno-histological appearance of four premalignant polyps was similar but the scattered fluorescent cells were more numerous. In eight benign polyps, however, staining was fairly uniform in all cells of the acini, and, though dimmer, showed much the same distribution as in normal mucosa. Lymph-node metastases from ten cases did not stain. The staining differences, which appear to portray an intrinsic distinction between benign and malignant states, may prove to be of diagnostic value. in the later stages, from the Medical Research Council. We are indebted to our surgical colleagues at Aberdeen Royal Infirmary and Woodend General Hospital for providing surgical specimens, and to Dr. C. M. M. Begg for advice about the possible cytogenetic implications of the antigen loss. Spinal osteoporosis is characterized by a loss of trabecular bone which in turn causes a reduction in radiographic bone density. In severe cases …