Not because cancer studies actually are reproducible, but rather because the reason they are not so often reproducible often comes down to the high complexity of the disease.
You grow your HCC1139 cell line in your lab, with your own supply of reagents, and you might get very different gene expression profiles of a lab in a different country growing HCC1139 cell lines on their own supply of reagents. There's so many subtleties in what is going on underneath in these systems that getting them right is insanely hard.
We don't know all the inputs, all the variables, that influence results. Getting the same result in one lab three times doesn't mean that another lab will get exactly the same results. But until we publish the results, we won't know what does and doesn't reproduce, unless there's that stake in the ground and a concerted effort to spend the highly limited time focused on pushing forward the boundaries of knowledge, we won't know.
So even if a broad range of hundreds of wet lab techniques, across thousands of experimental systems, doesn't always get the same result in different hands, unless we start to push at the amount of detail going on we'll never understand how to start to treat all these things.
Anyway, that's my rant, and I can understand why outsiders are concerned about individual cancer research experiments not reproducing at a very high rate, but I think it needs to be placed in this sort of context, where we only have measurement tools for a tiny fraction of what's going on, and need to still discover all the unknown unknowns.