Only w/ microscope. Palpating the breast may show a lump. It is not possible to determine exactly what the lump is without a biopsy. To determine when a biopsy should be considered, docs consider patient age, prior history, whether the lump is changing or is associated with other signs like dimpling, family history and some other personal factors. A mammogram can increase or decrease concern as well.
See a MD. Although breast cancer lumps tend to be hard and fixed to the chest wall, there are many exceptions in early cancers. Don't try to "guess" if it is cancer or not- see a md for an accurate assessment.
Get checked. Only a doctor can determine that.
Examination. You would need to see your doctor. Depending on your age, mammogram and/or breast ultrasound may be indicated. Breast nodules can be solid like a lymph node or fibroadenoma, and some can be cystic or full of fluid.