I don't know who Alex To is. I generally agree with cautious approach regarding drug candidates, espeically oncology drugs. XL184 has a long way to go. However, I have to criticize some of his points:
the fact that the company has just found out the drug has efficacy signals in these common cancers after the drug has been in development for so many years is baffling
This is not surprising at all. Traditional phase I oncology trials don't necessarily get all efficacy signals. They typically only entered a few patients in each type of cancer. I have to give EXEL credit for the RDT decision. In drug development, sometimes you have to think outside of the box. Doing one here with BMY objection was bold move from EXEL.
one has to put XL-184 in the category of the more toxic cancer drug candidates in development. That might partially be the reason why both Glaxo (GSK) and Bristol (BMY) gave the drug back to EXEL. For CRPC, the patients have relatively long life expectancy, compared to other more deadly cancers. Therefore, the life threatening adverse effects will be a consideration.
I really don't know where this comes from. XL184 is in more toxic cancer drug category? There is certain concern on safety for sure, but more toxic? Most patients in RDT had gone through CHEMO. As of CRPC, XL184 is going for docetaxel and/or Cabazitaxel patients at this stage. Talking about toxic, you can't get more toxic than docetaxel!