I agree with the last two PP. If someone kept asking all the time, I would probably say something along the lines of "there's nothing new to report since the last time (or if it's really frequent, say the last ___number of times) you asked."
For really pushy folks, I might go so far as to say something like "I appreciate your interest and support, but your frequent inquiries have started making me uncomfortable, so I'd rather not discuss this topic any more. I'll be sure to let you know when there's happy news to report."