ASCO closed out this morning with a couple of interesting sessions. The first was on cancer stem cells – how can we best target these elusive cells that are at the core of ongoing tumor growth and recurrence? Pioneering work in this area began in breast cancer but has expanded to many other areas. Stem cells in tumors have a lot in common with the stem cells that are present in embryonic development – the tumor stem cells appear to express developmental markers such as hedgehog, Wnt and Notch (touched on in Saturday’s blog) and these markers are being targeted with drugs to block their function and hopefully kill stem cells and prevent tumor recurrence. Though side effects come from the fact that these drugs will target other stem cells in the body doing normal functions such as in the gastrointestinal track, management of these is being addressed. One of the reasons that pancreatic cancer is so devastating – with the average lifespan following diagnosis being around a year – is that the stem cells in the tumor are really persistent and actually seem to thrive and multiply after treatment with the current standard therapy for pancreatic cancer, gemcitidine. The biology of these stem cells is becoming more understood though and this has led to the concept of a double whammy approach where following gemcitidine treatment tumors are treated with hedgehog-targeted drug which has shown good results in mouse models blocking tumor metastases from human xenografts. Notch-targeted drugs may also be introduced to this approach.
The final session I attended examined the side effects of blood vessel targeted drugs like bevacizumab and sunitinib including effects on heart and kidney function. These are somewhat rare but can be significant; as more patients are on these drugs for longer they are being closely monitored and clinicians are figuring out how best to overcome side effects. This is important because as a take home message from ASCO 2009 it seems that though they are still being clinically assessed in many tumors types, using VEGF/blood vessel targeting drugs to treat tumors could fast become a baseline tool for tumor management onto which other drug treatments can be added, depending on the patients biology and tumor status. Hopefully this means we are heading in the direction of a move away from, or at least to a reduced use of, chemotherapy.
