Hello, You have a lump in the middle of the arm. There is also a large bruise around the lump. The bruise is starting to go away. Your symptoms are indicative of some insect sting or bite that caused the lump, bruise often occurs due to bleeding (leakage of blood due to sting / bite) under the skin. Apply a thin layer of ointment Thrombophob on the affected area, it will help to reduce the bruise. Antihistamine and analgesic help to reduce discomfort and inflammation. Take care of your hygiene to prevent spread of infection. Other medical conditions that can cause similar symptoms are injury, bone fracture, abscess with spreading infection, lipoma or lymphoma. You are suggested to get clinically examined by an oncologist. Get blood tests, investigations, biopsy if recommended done. You will be treated with medicines, or recommended surgery depending on the severity of your symptoms and seriousness of the pathology detected. Stay away from addictions if any. Get treated at the earliest. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Nupur K., General & Family Physician