I first came across chaga whilst reading Cancer Ward by Solzhenitsyn in the 70’s, the book was semi-auto-biographical, he wrote about chaga being a folk medicine for cancer.
Its botanical name is Inonotus obliquus
https://en.wikipedia.org/wiki/Inonotus_obliquus
excerpt:
Chaga has been used as a folk remedy in Russia and other North-European countries for centuries and it featured in Aleksandr Solzhenitsyn’s 1967 novel Cancer Ward[3]
Thank you very much.