Hi, Thanks for writing in. Hope you are feeling better and continuing in your fight against your cancer. The spleen is an organ which is part of the immune system. It is located under the diaphragm on the left side. The pain you describe in the left upper abdomen might be due to an enlarged spleen. You should get an ultrasound scan done to see for the spleen size. The spleen grows from the left upper abdomen to the right lower abdomen and appears like a firm lump or mass. The pain might be due to spleen enlargement if present. However the diarrhea is unlikely to be due to the spleen. Commonest cause of diarrhea in patients taking treatment for leukemia is common stomach infections. Please consult your doctor and take a short course of antibiotics and eat healthy home cooked food. Please do not worry.