This sloka from Narayaneeyam (Dasakam 8, Sloka 13) is a Very powerful sloka that has been recommended by Sankaracharya for curing cancer.
अस्मिन् परात्मन् ननु पाद्मकल्पे
त्वमित्थमुत्थापितपद्मयोनि: ।
अनन्तभूमा मम रोगराशिं
निरुन्धि वातालयवास विष्णो ॥
Asmin paraathman nanu paadmakalpe
Thvamithamutthaapitha padmayonihi I
Anantha bhoomaa mama roga raashim,
Nirundhi vaathaalaya vaasa vishno. II
அஸ்மின் பராத்மன் நனு பாத்மகல்பே
த்வமிதமுத்தாபித பத்மயோனிஹி
அனந்த பூமா மம ரோக ராஷிம்
நிருந்தி வாதாலய வாச விஷ்ணோ
Sir can I chant this mantra for the sake of my father?
I would’nt know that. However, if I were you I would chant. I cannot cause any harm.
According to our Guruji go for mass prayer with this mantra for 16 or 32 times. It will have tremendous effect.
My brother suffering from bone cancer.. shall I chant this mantra for him
Yes, this has been recommended by Sankaracharya.