CD44ex10 transfectants are more likely to form local tumors in nude mice. Two to four independently derived vector-only, CD44ex10, CD44H, CD44ex7-14, or CD44ex10-14 Namalwa transfectants were injected SQ into nude mice. Animals were subsequently followed for the development of local tumors. The data represent a summary of three identical experiments in which a cohort of three animals received one of the indicated independently derived Namalwa transfectants (vector-only_{I, II, II or IV}, CD44ex10_{I or II}, CD44H_{I or II}, CD447-14_{I or II}, or CD44ex10–14_{I or II}). The incidence of local tumor development was significantly greater in animals that received CD44ex10 transfectants than in animals administered vector-only tranfectants (CD44ex10, 78% v vector-only, 38%, P = .01), whereas animals injected with either CD44ex7-14 or CD44ex10-14 transfectants had a significantly lower rate of local tumor development than that of animals administered vector-only transfectants (CD44ex7-14 6% or CD44ex10-14, 6% v vector-only, 38, P = .03). The incidence of local tumor development associated with a given CD44 isoform or vector-only was determined by averaging the rates of local tumor development of multiple independently derived clones: vector-only, four clones; CD44ex10, two clones; CD44ex7-14, two clones; CD44ex10-14, two clones; CD44H, two clones. P values were calculated using a 2 × 2 Fisher's exact test.