Depends on the goal. There may be another way to develop a cancer vaccine, but there may not be another way, which saves as many lives.

Thought experiment:

Consider the scenario that there isn't another method of conducting these scientific experiments. How many human lives would you sacrifice if it meant saving a lab animal? What's a fair rate of exchange for you? What if you yourself had an incurable, terminal illness that would have been curable if animal testing was available?

I don't mean to imply that one must have all the answers to criticize an injustice, but cheap throw away lines like "There's always another way" or "Not with that attitude" reek of shallow moralizing more concerned with virtue signaling than coherent ethical belief.

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How can we prepare scientific studies to be safe for human trials? I'm not disagreeing but with medical science there's not a lot of ways

Unfortunately--and as much as I wish it were otherwise--sometimes there really is only one way. And the reality is that you can't test medicine effectively on non-living things.