Now you see them, now you don’t? In our pioneering active surveillance program for small kidney tumors (Delayed Intervention and Surveillance for Small Renal Masses, or DISSRM Registry), Brady researchers are documenting something no one knew existed: very small renal masses that just seem to go away. Then, some of them come back – but some of them don’t.

“In our growing experience with active surveillance, we have encountered this unique phenomenon in about 5 percent of patients,” says Arnav Srivastava, M.D., lead author of a study recently published in the journal, Clinical Genitourinary Cancer. With co-investigators Alexa Meyer, Phillip Pierorazio, Steven Rowe, Mohamad Allaf, and Michael Gorin, he documented this “spontaneous clinical regression,” or disappearance.

“These patients have at least one surveillance image showing no small mass in the kidney,” says Srivastava. In about half of these patients, the tumor shows up again on the next imaging test. This might be explained by “limitations of our current imaging technology,” he continues. However: “the other half of patients had their small renal masses remain undetectable for extended periods of time, or even permanently.”

Good news for the patients whose tumor – usually smaller than 1 cm – reappeared: none of these masses grew rapidly, “and all these patients were alive after five years.”

What about the ones that stayed gone for good? Good news there, too, says the study’s senior author, Pierorazio, Director of the DISSRM Registry. “Small renal masses that permanently disappear remain an area of great interest for the Kidney Cancer Team. “We don’t know if these are benign lesions that just disappear on their own, or if they are small cancers that the body fights off.”