The drones are expendable. Just ask the Queen Bee of any hive, or the Mothership of any B-movie alien invasion. As long as you have a progenitor, being down doesn’t mean you’re out: given time, you can always rebuild your army.

In turns out that in the war on cancer, our adversary may act the same way. During Big Think's recent panel on the development of cancer research, Dr. Siddhartha Mukherjee, Assistant Dean of Medicine at Columbia University and author of last year's explosive tome, "The Emperor of All Maladies: A Biography of Cancer," asked his peers to define the breakthrough “cancer stem cell theory.” This stem cell research may explain why certain cancers, such as leukemia or lymphoma, appear to respond to treatment, only to recur after a period of remission.

The threat that cancer can return, even after apparently successful chemotherapy and radiation, remains terrifying. Why won’t it just go away? To understand the answer, one must first examine the depth and scope of a stem cell’s potential. In humans, for example, stem cells essentially contain the most basic characteristics of all the cells in the body. This means they have the ability to become, divide, and renew virtually any type of cell: a liver cell, a kidney cell, a blood cell. Previous cancer models assumed that all cancer cells are capable of generating tumors, but according to this new theory, cancers cells (for certain cancer subtypes, at least) exist on a hierarchical spectrum with stem cells on top. If therapy doesn't manage to kill this mother cell, the disease could be regenerating even while medical tests show that the cancer is in remission.

Dr. Lewis Cantley, Professor of Cell Biology at Harvard University, explains it thusly: “Some of the therapies that look like they're working beautifully because [they] reduce the total number of cells by 98% [are not] killing the ones that are keeping this tumor going, so that is why there is so much excitement about this. We need to get therapies that hit the cancer stem cells, not just the ones that are descendants of it.”

“The question is, can any cancer cell lead to a recurrence?” asks Dr. Harold Varmus, Director of the National Cancer Institute. If only certain cells have this ability, “it’s not enough to measure the total bulk of cancer cells.” Suddenly it is cell quality, not quantity, which matters.

But the research of how to actually target these cancer stem cells is still in its early stages, making this new revelation as unsettling as it is thrilling to both patients and doctors alike. Especially since these stem cells are tough. “It’s thought that those are the cells that are resistant to therapies,” adds Varmus. “One facet [of this] is so called drug resistance, which is a huge problem in cancer therapy today.”

If knowledge is power, then medicine has potentially gained a great advantage over cancer. But since doctors have not yet discovered how to target and destroy cancer stem cells, over the next several years they will seek solid footing on unfamiliar ground, even if they are a step closer to the cure.

More Resources:

— "The Evoloving Science of Cancer Stem Cells," a National Cancer Institute special report

— MedicineNet article on stem cells

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