One thing clear what you have said about lagna. When lagna & lagnesh are weak and Saturn has aspect on the lagna or lagnesh, a long term disease state always strikes.
In the natives case his lagnesh is in 8H, lagna is aspected by mangal & sani. Sani is the 12H lord also which is the house of disease & is also retrograde. Mangal does governs the head & tumour comes from sani or rahu & lagnesh is also weak aspected by rahu.
Another point to be noted is that Moon governs the immunity level of the body. It is also weak as it is conjunct with Saturn & mars. Saddi satti is also in its second phase. Natal sani & transit sani is also aspecting the lagna.
Now coming to the positive points, sun in the natal chart is not weak. Jupiter in transit is in lagna. These two points will help the native to come out of the his health problems.
Mantra chanting will not help, this requires yagyas & also wearing the requisite gemstones. This is an expensive process. But certainly it will help the native coming out of his health problems.