I had a kidney transplant 33years ago. Since a year or so my muscle mass is clearly reducing. I lost 10kg over 2years but now I am stable. My age is 58. My BP is reasonably under control and blood test for transplants OK. Creatinine is 1.2mg. Platelets are on the lower side of normal since many years and HB is less than normal for some years. They suspected a cancer but CT, MRI etc were all normal
Since you said all the blood tests and scans are normal nothing alarming is present. But bone marrow examination is also necessary since you said He and platelet count is low. If bone marrow aspiration and biopsy are normal nutrition disorders are the most common cause of weight loss. Concentrate on good nutrition and don't worry of cancer