Is there tenderness also (pain on pressing)? Is there any redness? Does the pain increases on change of posture and chest movements? Were any investigations done? What are the medications you are taking?
The assessment of these kind of pain starts with first to diagnose the tissue involved(say skin, tissue just below the skin, called as subcutaneous tissue, muscles, ligaments, bones, joints and organs), and then the pathology (infective, inflammatory, allergic etc). A long standing pain of this sort is likely due to the tender points or trigger points. The other possibility is costochondritis which is inflammation at the junctions of rib and cartilage or with the breast bone. Anti-inflammatory analgesics (Ibuprofen), local analgesic ointment, or spray, chest brace and warm compresses are helpful in this. Another possibility is muscle sprain. Tenderness usually points towards muscular and skeletal (bony/joint) conditions. Read about the costochondritis, in this resource;
A trigger point responds to the deep electrotherapy (done at physical therapy centers) like phonophoresis and iontophoresis. An evaluation by chest x-ray and personal examination is essential to pin point the causative and diagnosis.
Hope this helps.
Please feel free for your follow up questions.
A cancer is most likely to have a lump. Pain is not a common feature of the malignancy. So, if you don't feel a lump, chance of malignancy is not likely. Soreness, as I mentioned would be fibrofatty trigger point.
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