Why is testicular cancer so responsive to chemotherapy, even after it metastasizes? It's because of the stem cells, according to a recent study. Defining why testicular cancers are so susceptible to chemotherapy could eventually provide insights for treating other, more resistant cancers. The Cornell researchers' study also helped confirm that risk for testicular cancer is determined in utero. The research offers some evidence to support a hypothesis that, in humans, testicular cancers are initiated during embryonic development and lay dormant for 18 to 35 years.

"The study provides new insights into the basis for the responsiveness of testicular cancer to chemotherapy, which has always been an intriguing observation, but the basis for it was not clear," said senior author Robert Weiss. Most types of tumors contain distinct populations of cells. A small fraction of these are stem cells, which have the ability to grow new tumors from a single cell and - in most cancers - are extremely resistant to therapy. Often, other types of tumor cells are killed off during treatment, but cancer stem cells survive, then drive relapse by re-growing new tumors.