αImmediately after surgery, cells were placed in culture and GJIC examined (see Methods, Figure 7). After 8-10 weeks in culture, most of the tumor cells had died while the fibroblasts present in the initial suspension predominated. These cells did not express cytokeratins, contrary to tumor cells . The fibroblasts shown were derived from the moderately differentiated adenosquamous carcinoma tumor above (Figure 3, c-d). GJIC was examined as in Table1, at 3 days after confluence.