That's very sad. Have you considered writing to your son? Maybe just about your diagnosis and current medical situation rather attempting to persuade him to be "on your side"?  Maybe suggest meeting on neutral territory? It may be that he's scared about what's happening to you? I don't have any experience of your situation though sadly plenty of experience with cancer. 

I do hope you can establish communication.

Helen

Thank you, for your reply.

I am going to write him letters in a book, that won't be sent but will be there to show that I always love and think about him.

I am going to write a dated entry - nit necessary every day, just when there is something funny or something I  think he will be interested in etc.

He sadly won't meet me, and considers even neutral people to be influenced by me. 

Fingers crossed for a little light in this tunnel.

The book sounds like a good idea. 

Are you able to send him birthday/Christmas cards? I think keeping the communications open at your end is perhaps all you can do right now. Is it worth getting someone else to write the envelopes in case he knows your handwriting? I wish I had more suggestions. Have you thought about counselling to help you with this impossibly sad situation?