The KC-46 tanker aircraft (the U.S. military's designation for the 767s it uses as tankers, and which every other country calls the KC-767) uses an early version of an MCAS.1 This was ostensibly developed to cope with shifts in the aircraft's weight and center of mass during aerial-refuelling operations:
... The KC-46 uses a similar system because the weight and balance of the tanker shifts as it redistributes and offloads fuel. The KC-46 has a two-sensor MCAS system, which “compares the two readings,” the Air Force said.
However, even though changes in weight and balance as a result of onloading, transferring, and offloading fuel are common to all tankers, and, yet, the KC-135, KC-10, KC-130, KC-30, et al, do just fine without any MCASesque system.
What makes the KC-46 special in this regard?
1: The KC-46's early-model MCAS was later developed (incompetently) into the MCAS version used on the 737 MAX.