You need to read the Golden Light Sutra five times, with strong bodhicitta.

Also do strong purification with Chenrezig. Visualize beams purifying all the four things—negative karma, defilements, sickness and spirit harm—and the cancer. You need to do a minimum of four malas a day of the Chenrezig mantra, OM MANI PADME HUM. 

Recite one mala of Vajra Armor mantra each day. Continue this until you get better.

[Please note: Advice posted on the LYWA website is not a substitute for medical advice, diagnosis or treatment from a doctor or health care professional. If you have health concerns, do not disregard medical advice or delay seeking it.]