Test his stomach function for sufficient acid production. Question him about any reactions he has in his stomach such as discomfort, heartburn or any abnormal reactions. ALL cancer patients have disrupted stomach function which adversely affects normal methylation processes which promote cancer development. Do what you can to promote normal stomach function. This can be difficult, especially if there is a urease positive stomach infection. BTW helicobacter pylori is not the only bacteria which infects the stomach but is the only currently recognised one. Triple therapy such as used for helicobacter will not destroy these other bacteria, they are highly resistant. They protect themselves with a biofilm which causes large food molecules to enter the bloodstream which the immune system reacts against. Some people get autoimmune illnesses and some later get cancer.
It might be worth looking at iridology and an iris chart to see if there is anything in the small intestine which is stuck against the wall of the intestine. This affects the immune system function in the area and could make cancer far more likely. You could also look for a darkening in the spinal area, which looks like a grey marking but is actually a reduction in iris fibres revealing lower layers of the iris making it look darker. When this happens, the immune system control in the area becomes very weak. A situation which would prevent the immune system dealing with a cell which became cancerous. This can lead to autoimmune attacks against the area when "leaky gut" is present, a term that I dislike because it is actually leaky stomach which puts blinkers onto people's eyes and they waste time attempting to treat later stages of the digestive system.
Be aware that surgery does affect the nervous system and can cause the normal tone of the digestive system to change. The digestive system in the area connected to the surgery will often expand outwards caused by damage to nerves and anaesthetics. The autonomic nervous system is represented by a ring which is usually a third the way out from the pupil. It is this ring which represents the shape of the digestive system and how food moves through. Black marks just inside this are meant to represent stuck faecal waste, this becomes more common when there are pockets or sharp indentations. This is also possible when there are nerve rings inside the digestive system. If this is present then the immune system in the area will be adversely affected.
A low powered magnifying glass (x3 or x4) can be helpful. Such a glass placed against a mirror can allow a person to look at their own eyes if they can focus up close.
Check for signs of under methylation and supplement as best as possible to supply methyl groups. Some people use MSM methylsulfonylmethane for this. There are other nutrients such as methylfolate and methylcobalamin and other foods and supplements which can be helpful.
There are many foods with strong anti cancer effects. I suggest that you search for them and add them to his diet.