Hello, I read your message and understood your medical issue. Considering the age of your father in law and his medical history that you mentioned to me (he is 87 years old, treated for colon cancer a few years ago, takes transfusions every few months); altogether, they put him at a higher risk for hypercoagulation or predisposes more for thrombosis. The symptom is unilateral meaning that only his right leg is causing disturbance like pain and being swollen. It is very likely that this is caused by a deep vein thrombosis. My suspicion becomes stronger when I read that these symptoms are installed in a short period of time. I suggest you send him to the ER because if it is too late this condition may lead to excessive ischemia of the leg tissue and he may loose his leg forever or have other systemic adverse effects. Send him to the ER to take the first step in treatment with anticoagulation drugs and others and to do further examinations of the leg vessels such as a doppler examination of the leg vessels and maybe a CT-scan. This results will distinguish if he needs surgery or not. Hope this is helpful for you. Wish fast recovery. Dr.Albana