Sorry, C~Q that was my own miscommunication. I was talking about coconut milk, rather than cows milk. As the others have pointed out breast milk is also very good...

Black salve ingredients are: Sheep Sorrel, Red Clover, Bloodroot, Pau D' Arco, Graviola, Galangal, Zinc Chloride, Pine Tar, Emulsifying Wax, DMSO, Wintergreen Oil, Stearic Acid, Polysorbate 20, Glycerin, Olive Oil, Charcoal and Purified Water.

So lets look at the ingredients:
- Sheep Sorrel is a herb. It is very high in Vitamin C. It is most probably the vitamin C in it that gives it any cancer fighting benefit.
-Red Clover is legume. It is high in oestrogen, and is quite commonly used in pharmaceuticals because of this. This ingredients inclusion in a cancer salve I personally find worrying. Most solid cancers are hormone driven and studies have shown that too much Oestrogen can cause DNA mutations and actually cause cancers to be more aggressive.
-Blood root is a highly toxic flowering plant that produces a compound close to morphine. This substance kills animal cells by blocking the action of Na+/K+-ATPase transmembrane proteins. As a result, applying bloodroot to the skin may destroy tissue and lead to the formation of a large scab, called an eschar. Bloodroot and its extracts are thus considered corrosive. Studies relating to this substance being used in salves have shown that "microscopic tumor deposits may remain after visible tumor tissue is burned away, and case reports have shown that in such instances tumor has recurred and/or metastasized"[1].
- Looking at these ingredients, my *guess* is that Pau D' Arco is one of the main active ingredients. It's a herb from South America, and has been shown to work against various parasites like malaria, schistosoma, and trypanosoma. How that applies to Cancer I'm unsure, but there is no reason he can't just drink the tea.
- Graviola is just another name for the custard apple. This *could* be the other active ingredient based upon vitro (as in test tube) tests of the active proteins and cancer cells. Whether there is enough of the active ingredient in the salve to make a difference is again unknown, but I can't see why he can't just eat it.
-Zinc Chloride is a skin and respiratory irritant according to its MSDS. What purpose it has in the salve I have no idea.
- Pine tar has been used in the past to treat some skin diseases, such as rosacea, eczema and psoriasis. However, the process of making the pine tar also creates a substance called dioxane. Studies done by the Agency for Toxic Substances & Disease Registry have shown that dioxane at high doses can cause kidney and liver damage, and has been proven to cause irritation to the nose and mouth when inhaled as vapor. It is considered corrosive.
- Emulsifying Wax would just a benign vegetable based binding agent.
- DMSO (Dimethyl sulfoxide) would act as the drawing and dispersing agent being a type of sulphur. Sulphur is a drawing agent that can reduce toxins (things that don't belong in the body like metals from vaccines, poisons from insect bites etc.) this is how epsom salts and chelation works, however DMSO can be very harsh, so much so it can also be used as a solvent. One study showed DMSO exposure to developing mouse brains can produce brain degeneration and this neurotoxicity could be detected at doses as low as 0.3 mL/kg within children, what effects this would have to an adult applying it near the brain I'm again unsure but I would be very cautious.
- Wintergreen Oil (methyl salicylate) is a bit like deep heat, and is a natural low grade bleaching agent. In pure form it is toxic, especially when taken internally. A single teaspoon is equivalent to more than 23 aspirin tablets. The amount in the blood stream will be less when used topically, but can still cause poisoning if great care is not taken.
- Stearic Acid is basically just fat, like the type they use to make candles.
- Polysorbate 20 is a detergent and emulsifier.
The rest are just everyday things and benign.

SO.... having looked at the above ingredients, I can see that theoretically there may be some substance behind why the salve might work in some cases BUT the theory does revolve around two elements your DP could just eat and drink and still probably have the same effect without all the high risk that comes with a LOT of the other stuff. I personally think adding some of the cancer fighting foods to his diet is the safer option, but that's easy for me to say when I'm not in that situation...

Out of curiosity, why wont he let them operate if they can? And what type of cancer? Is it just restricted to his ear or has it spread?

[1] McDaniel S., Goldman GD (December 2002). "Consequences of Using Escharotic Agents as Primary Treatment for Nonmelanoma Skin Cancer"