Timothy M. Weiner

Using a PCR-based cloning technique, we have isolated a series of DNA fragments coding for tyrosine kinases that are expressed in a metastatic human colon tumor, and have subsequently analyzed their expression pattern at the protein level in human tumors. We identified both the alpha and the beta forms of the platelet-derived growth factor receptor (PDGFR), axl and 8 other genes, including 3 cytoplasmic tyrosine kinases. To study their expression in human colon cancer, we performed Western blots of matched sets of normal tissues and of carcinomas from the same patient. These revealed that the alpha-PDGFR migrates predominantly as a 200-kDa band in 8/8 normal tissues, and as a 170-kDa band in 17/17 malignant tissues, as well as in colonic polyps, suggesting that expression of an isoform of this receptor may be a marker for the progression of colon cancer. Additional studies showed that the Axl receptor tyrosine kinase was expressed at 10-fold higher levels in a peritoneal metastatic nodule than in other normal and malignant tissues. Immunohistochemistry revealed Axl over-expression specifically in the malignant cells of the tumor. This indicates that over-expression and possibly a differential processing event of tyrosine kinase receptors may be involved in colon cancer, and that they are potential markers for the progression of this disease.

Small cell carcinoma of the ovary is rare in adolescence. The etiology of such tumors is unknown. Several reports suggest that transgenerational exposure to diethylstilbestrol (DES) may have deleterious effects on the genitourinary tract. The authors describe a 15-year-old girl with small cell carcinoma of the ovary whose maternal grandmother had been taking DES while she was pregnant with the patient's mother. This case, while anecdotal, suggests that a transgenerational history of DES exposure should be noted, and that granddaughters with persistent abdominal pain even during childhood may need evaluation for genital tract abnormalities.