If you kill all the cancer cells, can the cancer still come back? Yeah, and not because a new cancer has arisen.
A study in the New England Journal of Medicine (Sep 9), looks at myelodysplastic syndrome (MDS). I won't define the condition further than to say it means a pre-cancerous condition where blood cells are formed that are infeffective or abnormal. The condition used to be called "pre-leukemia:" there is the risk that this syndrome will progress to leukemia.
So, the difference is that MDS makes bad cells, leukemia is really bad cells multiplying out of control. No hematologist would agree with that; it's much more complicated. This half-baked definition just works for my purposes.
Because the jist of the article is, "OK, we can treat MDS with a drug that kills all the bad cells to the point where they are in remission and we can't find any of those cells. How come some of these patients have a recurrence?"
The simplistic answer is that the researchers found that stem cells which have a chromosomal abnormality that puts them at risk of producing ineffective MDS cells still exist in the body, and show a resistance to the drug.
For Onion Peelers,
Although lenalidomide [the cancer drug] efficiently reduced [stem cells that lead to MDS] in patients in complete remission, a larger fraction of the minor stem cells as well as functionally defined chromosomally abnormal stem cells remained distinctly resistant to lenalidomide. Over time, lenalidomide resistance developed in most of the patients in partial and complete remission, with recurrence or expansion of the resistant cell lines and clinical and cytogenetic progression.
You can see why knowing this is important. As the authors describe it,
The present findings have clinical implications, since the identification of distinct stem cells in myelodysplastic syndrome may provide a sensitive tool for surveillance during therapeutic targeting. The ability to pinpoint and purify minor cancer stem-cell populations, before as well as during treatment, might be useful in monitoring clonal evolution and in identifying molecular targets that are distinct from those identified in the bulk of the tumor.If we can identify the troublesome stem cell lines that lead to MDS, then they can be a marker and a target for therapy that could lead to more remissions and less recurrences.
The lesson to be learned is that treatment has to look beyond the immediate abnormal state to higher-order, or predisposing, elements in order to be successful. We're pretty good at killing tumor cells; we need to get better at dealing with the cells or conditions that lead to tumor cells.
An interesting piece of work.