The ailing son of a retired city cop is not only suffering from leukemia but also has an extremely rare form of bone marrow, prompting a desperate search to find a matching donor for him.

Brian Wecker, 15, the son of ex-NYPD Officer Christopher Hembury, has what’s known as “Philadelphia chromosome.” Without a transplant, Brian has only a 30 percent chance of survival, doctors say.

Bone-marrow screenings will be held Wednesday from noon to 6 p.m. at the Midtown North Precinct at 306 W. 54th St. and Oct. 18 at the Nesconset Fire Department on Long Island.