How can you tell the difference between a knot and a tumor on the back?

Both same: Both terms are inconclusive and refer to a palpable lesion not ulcerating but present in back region. The most common small knot or tumor is lipoma which is benign. If multiple and unchanging then watching for growth is acceptable. If firm and showing signs of enlarging then bx indicated since non specific lesions histologically can only be determined by microscopic exam for dx and margins.