This is not likely to be anything serious. The most common swelling of this kind are lipofibroma and neurofibroma. The are benign (non cancerous) swellings. No harm in getting an evaluation by your primary care physician.
Please feel free for your follow up questions.
We wrongly attach fear to the lumps or swelling. Majority of them are benign. A movable swelling is very likely to be benign. In the breast tissue; it would be fibroadenoma, which is again a non cancerous swelling and is quite common. Near to the breast tissue; these are likely to be composed of variety of tissue like fat tissue, nerve tissue, fibrous tissue etc. And in all likelihood to be benign.
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