We report on a 65-year-old female patient who was referred to our center with an intraosseous mass of the eighth rib and history of a fall on the left chest wall 2 months ago. A diagnostic outpatient chest radiograph was performed for pain in the left hemithorax, revealing a pathological fracture with an expansive osteolysis and unclear intraosseous of the eighth rib on the left lateral side. Following additional computed tomography (CT) and magnetic resonance imaging (MRI) scans, the patient was referred to our sarcoma center.
At the time of presentation, almost 3 months after the fall, the patient no longer reported any symptoms. Pain or shortness of breath was denied, as well as B symptoms or a known tumor disease. The clinical examination showed normal soft tissues on the left hemithorax without triggerable pressure or chest compression pain, a tumor in the area of the ribs/chest wall was not palpable.
External X-ray diagnostics showed a pathological fracture of the eighth left lateral rib with an unclear osteolysis (Figure 1(a)). The CT scan of the ribs showed an expansive, osteolytic intraosseous lesion, 3 x 2 cm in size, with a sclerotic rim and accompanying pathological fracture of the eighth rib on the left lateral side (Figure 1(b)). Similarly, the MRI of the thorax demonstrated evidence of a contrast medium-enhancing lesion without a significant surrounding reaction (Figure 1(c)). A staging CT of the thorax, abdomen, and pelvis showed an arterial hypervascularized lesion in the liver, which was constant in size in the CT follow-up controls. There was no evidence of further lesions. No abnormalities were found in the laboratory blood chemistry examination.
After presenting the findings to our interdisciplinary tumor board, a biopsy was indicated. For this purpose, a CT-guided biopsy of the mass was performed. Histologically, there was a spindle cell lesion with mild nuclear atypia and pleomorphism with included trabecular bone. The immunohistochemical examination revealed a strong diffuse-positive immune reaction for vimentin, a nuclear-positive immune reaction for special AT-rich sequence-binding protein 2 (SATB2) (partial) and a positive immune reaction for smooth muscle actin (SMA) in the absence of the other markers (Pancytokeratin, S100, CD34, desmin, beta-catenin). Due to the only sparse sample material that was submitted, a further molecular pathological examination was not possible, so that a further classification of the lesion was not possible and an open re-biopsy was recommended. The samples obtained again showed an indicated biphasic neoplasia consisting of fascicular or cell-rich areas next to cell-poor, increasingly hyalinized, or chondroid-appearing areas without higher-grade cellular atypia, which was differentiated myofibroma-like from the histological aspect (Figure 2(a)-(d)). Mitoses were not clearly displayed. However, the performed Ki67 proliferation index showed an inhomogeneous proliferation activity with a Ki67 proliferation index of up to 15% detectable in the hotspots. The lesional cells only showed an immunohistological expression with the antibody against sm-actin. Furthermore, a (possibly unspecific) expression of SATB2 was also found. The remaining immunohistological tests (antibodies against beta-catenin, CD34, desmin, S100, STAT6) were negative again (Figure 2(e)). An insertion in exon 11 of PDGFRB (p.I538_L539insR) could be detected by molecular pathology. This variant was classified as probably activating in vitro (Figure 2(e)) so that in the absence of other tumors, the diagnosis of a solitary intraosseous myofibroma was finally made activating PDGFRB mutations represent a characteristic molecular alteration in these lesions. MDM2 amplification was not present, so that a low-grade osteosarcoma could be ruled out. There was no evidence of malignancy in the material available here.
Due to the lack of symptoms, the patient decided against surgical treatment. The CT follow-up after 3 months showed an unchanged lesion of constant size, which is why the patient continues to favor conservative therapy.