On my diagnosis paper it says: osteolytic lesion without sclerosis ring, with clear, irregular margins. could you tell me what is it in more detail?

Plasmacytoma?: Hard to say without more information, but an osteolytic lesion could be multiple myeloma, or if a single lesion, a plasmacytoma of bone. Most "solid tumor" cancers that go to bones are "blastic" and not "lytic" (like a punched out moth eaten area). Ask the doctor that ordered the test what it means. Additional laboratory (spep/if, flc, upep, b2m) testing and a biopsy of the area may be in future.