Solitary bone plasmacytoma is a rare oncological disease, which in this case manifested as an expansive lesion on the left ninth rib with recurrent, predominantly nocturnal chest wall pain.[1] Imaging initially suggested fibrous or osteofibrous dysplasia, but histopathology and immunohistochemistry confirmed the diagnosis of solitary plasmacytoma of bone.[1] Pacient podstúpil chirurgickú resekciu postihnutého segmentu rebra.[1] The patient refused the recommended adjuvant radiotherapy, which could improve the prognosis.[1] 21 months later, the disease progressed to multiple myeloma, a complication that occurs in some patients with solitary plasmacytoma.[2] Unlike solitary plasmacytoma, which is localized to one area, multiple myeloma affects many areas of the bone marrow and causes widespread problems, including anemia, bone destruction, kidney damage, and high calcium levels.[2]