Valerie Harper Rips Broadway Honcho -- How Dare You Accuse Me of Hiding My Cancer!

No one was more shocked by the return of Valerie Harper's cancer than Valerie Harper -- so she insists in new legal docs, claiming the Broadway playwright who accused her of keeping her cancer a secret is wrong beyond measure.

TMZ broke the story, Matthew Lombardo -- the playwright behind the Broadway production "Looped" -- sued Harper for $2 million, claiming she withheld the truth about her cancer's return in 2012.

Matthew claims Valerie's ruse eventually fell apart when she was forced to pull out of the play because of her medical issues ... and it cost him $500,000 to find a last minute replacement.

Harper is now firing back, insisting Matthew's talking out of his ass. Harper claims Lombardo found out about her cancer's return the same time she did, so his lawsuit is baseless.

At the time, Harper claims she believed her cancer had been successfully removed during a prior surgery, and when her health began to deteriorate in early 2013, she thought she had suffered a stroke. It was only later she discovered her lung cancer hadn't just returned, it had spread to her brain.