Tim Keller's health has shown "remarkable" improvement as he continues to fight stage 4 pancreatic cancer. 

The pastor's wife Kathy shared the update on Twitter in which she also thanked supporters for their continued prayer. 

"Through God's mercy and your prayers, there has been remarkable improvement in the last 18 months — in fact, his doctors are using words like 'fantastic' and 'dramatic' to describe the progress. Your prayers are working!" she wrote.

"As Tim's begins a new round of chemotherapy this week, we hope you will pray for continued effectiveness of the treatment with even fewer side effects.

"Thanks again for the outpouring of love and support. We are grateful and ask for your continued prayers."

Keller is the founder of Redeemer Presbyterian Church in New York and the author of a number of popular Christian books, including "The Reason for God" and "The Meaning of Marriage". 

He was diagnosed with cancer for the second time in May 2020, having previously beat thyroid cancer in 2002. 

He has since undergone successive rounds of chemotherapy. 

Throughout his cancer battle, Keller has spoken candidly about his experience from the perspective of his Christian faith, and asked for prayer that both he and Kathy would stay faithful throughout. 

"Pancreatic cancer is able to learn how to evade medication, so it is only God's power that we look to for complete healing," he said in the summer. 

"Please do pray that I will be able to fulfill my teaching and other obligations, and that the neuropathy and other side effects will be minimal while the medication will be effective against the cancer, and that we will run the race God has set before us with joy."