Piece of the Puzzle = key factor?

Not necessarily a key factor.
If we use the information gained (protein that interacts with RNA) and add it to other information gained it may provide us with a better understanding of what to do to cure cancer.

Puzzles can have lots of pieces. Some are minor, some are major (the center of a character's face).

But every piece of the puzzle helps.

Thank you both.

But in the context, it says "major cancer-research breakthrough". That is why I deemed it was about "key factor".

Key factor would mean the one piece of the puzzle that ties everything else that has been learnt together.
It is not clear from the paragraph that this one particular breakthrough is in fact THE key factor.
It could in fact be A key factor but this is not clear.

If you are translating this it would be unwise to put more emphasis on the breakthrough than is otherwise implied.

Thanks for reminding me of that.