The intriguing patterns of tumor response to trabectedin.

Among soft tissue sarcomas, myxoid liposarcomas are exceedingly sensitive to trabectedin. Obvious tumor shrinkage is seen in some patients, whereas nondimensional changes in tumor tissue are seen in others especially after the first cycles of therapy. These patterns of tumor response are reminiscent of the way in which solid tumors respond to targeted therapies. The finding of trabectedin's ability to target the FUS-CHOP-mediated transcriptional block, restoring adipogenic differentiation within the tumor in myxoid liposarcomas, confirmed a 'targeted' activity that differs from its well-known atypical alkylating mechanism of action. Uterine leiomyosarcoma may show similar patterns of dimensional and nondimensional responses to trabectedin. Unusual cases of delayed response are occasionally seen and suggest other mechanisms of action, including activity on the tumor microenvironment which has recently been reported. An intriguing question is whether the different patterns of response have clinically or therapeutically meaningful correlations.