Final answer:
The most concerning symptom is a nontender lump in the right groin.
Step-by-step explanation:
The symptoms described suggest potential complications of the drug cyclosporine. One of the most concerning symptoms in this case would be the nontender lump in the right groin, as it may indicate the development of acute graft-versus-host disease (GVHD) after a bone marrow transplant. Acute GVHD can cause tissue damage and lead to a cytokine storm, which can be life-threatening. It is crucial for the patient to seek immediate medical attention to determine the cause of the lump and receive appropriate treatment.