God knows it hurts to see loved ones with diseases like cancer, or with any sort of physical or mental condition. But, just like those who lack other things, He will give you and them the strength to get through it.
Job’s friends were wrong to blame Job’s sickness and other problems on Job’s sin. But, the presence of death, sickness, and so on is because sin entered the world, and death by sin. (Romans 5:12) Things get damaged, wear out, and so on, and that includes our bodies. Sadly, sickness is a part of life that we must overcome.
God can heal a person, of course, if it’s His will. Don’t get like Job’s friends. It’s not a lack of faith or sin that keeps people from being healed. Sometimes, God’s perfect plan is for a person to be sick. For instance, a person in a hospital might wind up inspiring someone else who doesn’t have that faith.
We can pray for an end. Paul prayed three times for the “thorn in his flesh” – what most think was a severe vision problem – to be healed, but God said Paul’s strength was made perfect in weakness. (2 Corinthians 12:8-9) In other words, by Paul being able to travel and preach and endure all he did, it was showing God’s strength to get him through it. It kept the emphasis on God, not on Paul.
Sometimes, God wants to heal. However, “healing ministries” aren’t Biblical. If a person could heal like they claim, there would be no sickness ever. Jesus healed a child whose father didn’t believe. The father simply asked Jesus “help my unbelief,” meaning he knew he needed Jesus’ help for his unbelief to become belief. (Mark 9:24) Many times, these people simply want glory for themselves. They put the focus on the miracle, not where it belongs – on Jesus.