“He could not imagine any greater joy than to go away into the woods for months on end, to break off this chaga, crumble it, boil it up on a campfire, drink it and get well like an animal. To walk through the forest for months, to know no other care than to get better! Just as a dog goes to search for some mysterious grass that will save him . . .” From The Cancer Ward by Aleksandr Solzhenitsyn
 Chaga is a parasitic growth found on birch trees in frigid regions of the world. The fungus takes up a large amount of betulin, some of which it converts to betulinic acid. Birch bark tea will contain betulin, but inconsequential betulinic acid.
 Unlike betulin, which has poor bioavailability, the triterpene betulinic acid is said to be bioavailable.
A hot water extract is required to break through the chaga chitin & release the betulinic acid. Powdered chaga is probably the best bet. I would simmer the powder in water for 5 hours. The strained tea will keep well in the fridge.
The infusion will contain a mix of triterpenes .
Some years ago I came across an analysis of betulinic acid from chaga collected from birch trees in various locations. Siberia-sourced seemed the best bet - if one could trust the supplier. U.S. chaga didn't look to be promising, based on climate. I found a Canadian source, wild-harvested from trees in the far north. Tried it for a long while, until it was edged aside by other supplements. Didn't reorder.
In a 2014 Chinese paper, Finland-sourced looked to be promising .
 Betulinic Acid studies.
[5a] (2007 - Netherlands)
"Broad in vitro efficacy of plant-derived betulinic acid against cell lines derived from the most prevalent human cancer types."
"After 48 h of treatment with BA, cell viability ... and cell death ... showed clear differences in sensitivity between cell lines. However, in all cell lines tested colony formation was completely halted at remarkably equal BA concentrations that are likely attainable in vivo. Our results substantiate the possible application of BA as a chemotherapeutic agent for the most prevalent human cancer types."
[5b] (2007 - U.S.)
"Betulinic acid is a pentacyclic triterpene natural product initially identified as a melanoma-specific cytotoxic agent that exhibits low toxicity in animal models. Subsequent studies show that betulinic acid induces apoptosis and antiangiogenic responses in tumors derived from multiple tissues; however, the underlying mechanism of action is unknown. Using LNCaP prostate cancer cells as a model, we now show that betulinic acid decreases expression of vascular endothelial growth (VEGF) and the antiapoptotic protein survivin."
[5c] (2008 - U.S.)
"Betulinic acid suppresses constitutive and TNFalpha-induced NF-kappaB activation and induces apoptosis in human prostate carcinoma PC-3 cells."
[5d] (2011 - S. Korea)
"BA significantly reduced cellular and secreted levels of vascular endothelial growth factor (VEGF), a critical angiogenic factor ... Furthermore, BA prevented in vitro capillary tube formation in human umbilical vein endothelial cells ... maintained in conditioned medium of hypoxic PC-3 cells, implying anti-angiogenic activity of BA under hypoxic condition."
[5e] (2013 - U.S.)
"Betulinic acid selectively increases protein degradation and enhances prostate cancer-specific apoptosis ..."
Why try it?
Hypoxia-inducible factor-1α (HIF-1α) is often active in advanced PCa, particularly when there is drug resistance. Inhibition of HIF-1α [5d] will likely extend the duration of treatments. In addition, it will inhibit new blood vessel formation. It is the latter that allows tumors to grow.