Facing cancer once is daunting enough, but the shock of relapse can be crushing.

Three new studies now confirm what keeps tumors coming back is the so-called cancer stem-cell. If true, we can foresee therapies that greatly extend cancer survival.

Scientists have debated the existence of cancer stem cells, but the new evidence suggests tumors contain stem cells that are often dormant, shielding them from chemotherapy.

After treatment and given enough time, the surviving stem cells divide, producing more cancer stem cells as well as differentiating into the variety of cells found in a tumor. This ability to produce cells with varying characteristics may help explain metastasis, when cancer cells are able to migrate and invade other organs.

Researchers in these new studies worked with tumors in the brain, skin and gut of mice. One group found a way to label brain tumor stem cells, track them, and saw they survived chemotherapy. But when researchers repeated the experiment with a genetic trick that prevented stem cell replication, the tumors shrank.

Other researchers focused on benign intestinal tumor cells that are the precursor to cancer. They labeled the cancer stem cells and introduced a gene that made them glow. The tumors they produced glowed the same color confirming the tumor cells came from the stem cells.

The last group of researchers labeled individual skin tumor cells and tracked them. Most tumor cells divided a few times before dying out. A tiny group of tumor cells continued to grow and divide which further supports the existence of cancer stem cells. These studies provide a powerful new approach to cancer therapy.