While Luna scored his second successive 67 in the Madeira Island Open for a two-stroke lead over Britain's Liam White, Russell slumped out of the event at 10 over par - 20 strokes worse.
The 37-year-old from Kent hoped his problems were behind him last May when a lymphoma in his chest was found to be benign. "I feel like I've been given a second start in life," he said then. But now four more growths have been found.
"I've been told the outlook is good, but I'm suffering panic attacks at the moment, I can't sleep and my temper is so short that I was advised to get away from my wife and kids for a while. That's why I'm here.
"I had one removed from the inside of my gum three weeks ago. I'm being monitored every five weeks and my next scan is scheduled for next Friday, but if I can get into next week's tournament in Gran Canaria I will put the scan off for a few days.
"I don't think I would have played the second round, but for the fact that my partners [Luna and Scotland's Paul Lawrie] were going so well. I didn't want to pull out and leave them as a two-ball because that could have affected their rhythm.
"I'd really like to take a year off and get myself fit again. I'm planning to speak to Ken Schofield [executive director of the European Tour] about the situation."
Luna said: "I could see David was struggling, but he never said anything about his problem. Playing today to help us was a really nice thing to do."
Scores, Sporting Digest, page 47