SGN-35C antitumor activity was evaluated in a xenograft model of heterogeneous CD30 expression consisting of a mixture of a BV-resistant Karpas-299 cell line mixed with parental Karpas-299 cells to assess bystander activity in vivo….A single dose of SGN-35C led to significant tumor growth inhibition in animals bearing lymphoma xenografts, including a BV-resistant model and a model of heterogeneous CD30 expression, demonstrating that SGN-35C can elicit bystander activity in vivo.