I'd write it as "The excised liver sections from two patients showed no histological evidence of HCC". I'd say liver sections here because if you excise the liver, then you have to transplant a new one. But if the excision was for a biopsy, then only a small section of the liver would have been removed. (I'm a medical editor and have been editing this kind of sentence every day for the past 15 years.)
If you say "They lead a happy life", it implies that they share their lives with each other, as, perhaps, a married couple does.
If you say "They lead happy lives", it implies that their lives are separate. I suppose, though, that some readers might insist it's possible to interpret the sentence as meaning that they each lead multiple lives because they have multiple identities (as in The Three Faces of Eve, a book about schizophrenia). Ergo, you might want to say "They each (now) lead a happy life", which implies that they are not related in any way, except that neither one has liver cancer.