Maken: What, in your mind, is the prime value in Objectivist ethics? "To hold one’s own life as one’s ultimate value, and one’s own happiness as one’s highest purpose are two aspects of the same achievement. Existentially, the activity of pursuing rational goals is the activity of maintaining one’s life; psychologically, its result, reward and concomitant is an emotional state of happiness."- Ayn Rand, "The Objectivist Ethics".
So either you think Objectivism would say that you should steal the guy's cure for cancer because "living" is the prime value, or you have to agree that having one's life as one's ultimate value and one's happiness as one's highest purpose would (as I think everyone should agree here) demand that you do not steal his cure. If you agree with Objectivism that the initiation of force is wrong, then the answer to your proposal is that no, you shouldn't steal the cure even though it could save your life. Regardless, your question doesn't highlight anything in particular about transhumanism, as transhumanism is not a philosophy unto itself, but a particular position in philosophy advocating the use of technology to expand our abilities and extend our lives for our own benefit. I haven't seen Hotu or myself say that survival at any cost is the goal in either Objectivism or transhumanism (some transhumanists might say that, but I have never heard of one).
I kind of think of it like this: Objectivists would fall in a "libertarian" place on a hypothetical political spectrum (by this I mean that, at the very least, everyone can agree that non-Objectivists would almost universally classify Objectivists as libertarians, whether or not the concept "libertarian" as well as "conservative" "liberal" and the rest are epistemologically justified, etc.). Similarly, an Objectivist is going to logically take positions in support of the development of any and all medical technologies to extend healthy life (with the obvious and I hope don't-actually-need-to-be-stated-explicitly restrictions against the use of force or fraud to achieve their development or use), as well as those that provide us with enhanced abilities of various sorts, etc. and so would be classified as a transhumanist by pretty much everyone else as a result of their positions. Now one can debate whether "transhumanism" is a valid/useful concept or not, just as one can about the names for various political orientations. But I think we can all agree that the support for the development and deployment of the sorts of technologies transhumanists call for (in the context of a free market absent any and all coercion) is an obvious application of Objectivist principles (whether or not one wants to call oneself a transhumanist).