Remember in your closing moments that pain is in itself a creation from Allah Ta'ala, and none can harm you unless it has been decreed by the Almighty Allah, and no disease can cause you harm, lest it has been decreed. None can benefit you lest Allah wishes it. Therefore, medicine is of no use unless Allah has ordained for you to become well. Like this, if Allah wills you to be well, then you shall be well.
Please brother, do not undertake in ChemoTherapy. It is extremely painful and may seem to add precious moments to your life, but these moments if you are to live them, then it is decreed, do not live these moments under immense pain of chemotherapy, live them amongst those you love and the pious. Let no one stand in your way in reciting the Kalimah. I wish for Allah to make you die a Mo'meen, and when your soul is taken from you, taken in such a way that it is like a feather being plucked. Remember that Allah is always with you. Who knows, I may die before you, I may be young, but my time is vastly approaching as is everyones. Make use of the littel time you have remaining to make preparations for the Eternal Hereafter.
May Allah bestow His Eternal Mercy and Shower His Countless Blessings on you, and you make of amongst the first to enter Paradise, and make your last breaths the Kalimah, and allow you to die the most honourable death, a death which is most pleasing to Allah Ta'ala. Ameen.