A man in his 60s presented with progressive right arm swelling and functional limitation. Plain radiographs demonstrated a large long-segment expansile lytic lesion of the humerus with a multiloculated "soap-bubble" appearance, raising concern for a primary bone tumor or metastatic disease. Magnetic resonance imaging showed a large marrow-based expansile lesion with cortical thinning, heterogeneous T2/STIR hyperintensity, patchy enhancement, and no fluid-fluid levels. The patient was lost to follow-up and re-presented 2 years later with symptomatic anemia, hypercalcemia, marked hyperglobulinemia, and a reversed albumin-globulin ratio. Repeat magnetic resonance imaging demonstrated interval enlargement with cortical breach and intra-articular extension into the elbow joint. Staging CT demonstrated disseminated lytic skeletal disease involving the axial and appendicular skeleton. Serum protein electrophoresis demonstrated an IgG kappa paraprotein, and bone marrow biopsy confirmed diffuse clonal plasma cell infiltration consistent with multiple myeloma. This case highlights that dominant expansile long-bone lesions with tumor-like morphology may represent plasma cell neoplasia and can closely mimic primary bone malignancy or metastatic disease on imaging.

The current study aimed to differentiate between benign and malignant medullary lesions in the appendicular skeleton of patients with plasma cell diseases using whole-body low-dose computed tomography (CT) and various clinical indicators. The clinical and radiological data of 234 patients with multiple myeloma (mean age, 59.5 ± 8.4; males: 128) who met the inclusion criteria and visited our hospital between December 2020 and February 2023 were retrospectively evaluated. A total of 234 lesions (1 lesion per patient) were categorized into plasma cell tumor (PCT; n = 154) and red bone marrow (n = 80) groups. Intergroup comparisons were carried out using the independent-samples t test, Mann-Whitney U test, or chi-square test. Variables exhibiting statistically significant differences (P < .05) were included in the receiver operating characteristic curve analysis to evaluate diagnostic accuracy. The sensitivity and specificity of a CT value ≥41.5 hounsfield unit (HU) as a diagnostic criterion for PCT were 94.2% and 91.8%, respectively, indicating a diagnostic accuracy of 93.5%. A well-defined boundary as a diagnostic parameter exhibited sensitivity, specificity, and diagnostic accuracy of 88.9%, 93.6%, and 88.7%, respectively. The sensitivity and specificity of the omitted variable (CT value ≥41.5 HU + well-defined boundaries) were 86.4% and 96.5%, respectively, indicating a diagnostic accuracy of 91.6%. CT value ≥41.5 HU and well-defined boundaries are excellent diagnostic variables for diagnosing PCTs.

A man in his late 40s presented with progressive chest pain, cough and dyspnoea. Imaging revealed left lung collapse with pleural involvement. Thoracoscopic pleural biopsy confirmed pulmonary adenocarcinoma by immunohistochemistry. Staging fluorodeoxyglucose positron emission tomography-CT demonstrated nodal disease and unexpectedly diffuse marrow uptake with widespread lytic lesions involving the axial and appendicular skeleton, raising concern for a haematological malignancy. Serum protein electrophoresis revealed no monoclonal band, arguing against plasma cell dyscrasia. CT of the brain demonstrated multiple lytic calvarial lesions without parenchymal involvement, an unusual pattern in lung adenocarcinoma. The patient was diagnosed with stage IV lung adenocarcinoma with extensive skeletal metastases. Owing to poor performance status and advanced disease, the patient was managed with the best supportive care and died 5 months after diagnosis. This case highlights that lung adenocarcinoma may rarely present with diffuse marrow involvement and highlights the importance of histopathological correlation when imaging mimics haematological disease.

Osteitis fibrosa cystica (OFC) is a rare skeletal complication of primary hyperparathyroidism (PHPT) that may present with multifocal osteolytic lesions mimicking multiple myeloma (MM) or metastatic disease. We report a 79-year-old woman with several years of generalized bone pain, fatigue, anorexia, and weight loss. Imaging revealed disseminated lytic lesions throughout the axial and appendicular skeleton, and MM was initially suspected. However, serum protein electrophoresis was normal, and bone marrow biopsy showed reactive changes with polyclonal plasma cells. She later developed a pathological midshaft femoral fracture. Laboratory testing showed severe hypercalcemia, markedly elevated parathyroid hormone, hypophosphatemia, elevated alkaline phosphatase, and vitamin D deficiency. Fracture fixation with targeted bone biopsy confirmed brown tumor consistent with OFC, and sestamibi scintigraphy localized a right inferior parathyroid adenoma. This case highlights that PHPT should be considered in patients with multifocal lytic bone lesions.

Low-grade osteogenic tumors in the appendicular skeleton can show overlapping radiologic and histologic features, especially when secondary aneurysmal bone cyst (ABC) change is present. Osteoblastoma (OB) with secondary ABC and low-grade osteosarcoma (LG-OS) with secondary ABC may be difficult to distinguish, and noncanonical molecular alterations such as KMT2D or ZRSR2 variants may further complicate interpretation. We present an 18-year-old male presented with 6 months of atraumatic hip/knee pain and progressive difficulty weight-bearing. Imaging demonstrated a proximal femoral intramedullary lesion with cortical thickening, impending breakthrough, and surrounding marrow/soft-tissue edema. The differential diagnosis included OB vs LG-OS. Two image-guided biopsies favored OB. The patient underwent wide resection with allograft prosthetic composite reconstruction; margins were negative, and overall pathology supported OB with secondary ABC. Recovery was uncomplicated aside from transient urinary retention. By postoperative week 8, the patient had progressed to full weight-bearing with minimal pain. CT chest demonstrated stable benign nodules under surveillance. The integrated radiologic, histologic, immunophenotypic, and molecular profile supports a low-grade osteogenic tumor with secondary ABC.

Heterogeneous response to anti-programmed cell death protein 1 (PD-1) immunotherapy in lung cancer necessitates reliable biomarkers for monitoring systemic CD8[+] T-cell dynamics. This study used [[68]Ga]Ga-NODAGA-SNA006, a CD8-targeted PET tracer, to evaluate CD8[+] T-cell distribution in relation to disease progression and treatment response. Methods: Fourteen patients with stage II-IV lung cancer underwent baseline [[68]Ga]Ga-NODAGA-SNA006 PET/CT and blood CD8[+] T-cell quantification. Eight patients receiving anti-PD-1-based chemoimmunotherapy underwent PET/CT and blood analyses before treatment and after 2 treatment cycles. SUVmax was measured in tumors (along with the tumor-to-background ratio), the spleen, the liver, and axial (sternum, T12, pelvis) and appendicular (femur) bone marrow. Correlations with disease stage, peripheral blood CD8[+] T-cell quantification, programmed death ligand 1 (PD-L1) expression, and tumor reduction were assessed. Results: Patients with stage IV disease patients exhibited a lower peripheral blood CD8[+] T-cell count and percentage (P < 0.05), whereas the SUVmax in the spleen (P < 0.05) and axial bone marrow (sternum, T12, pelvis; P < 0.01) was higher than that in patients with earlier-stage disease. Peripheral blood CD8[+] T-cell percentage was correlated with SUVmax in the spleen (r [2] = 0.38, P < 0.05) and axial bone marrow sites (most significant in sternum: r [2] = 0.68, P < 0.001). After anti-PD-1 therapy, analysis of combined "axial skeleton SUV" (sternum, T12, pelvis) revealed a significant interaction between time and PD-L1 group (P < 0.001): SUV increased in the low PD-L1 (<10%) group but decreased in the high PD-L1 (≥10%) group. Changes in peripheral blood CD8[+] T-cell count and percentage were not significant. Tumor shrinkage was not significantly correlated with peripheral blood CD8[+] T-cell percentage or T-cell dynamics. For all target lesions, tumor shrinkage showed moderate positive correlations with baseline lesion SUVmax (r [2] = 0.30, P < 0.01) and baseline tumor-to-background ratio (r [2] = 0.34, P < 0.001) and a strong positive correlation with the reduction in lesion SUVmax after treatment (r [2] = 0.44, P < 0.01). Conclusion: [[68]Ga]Ga-NODAGA-SNA006 PET/CT revealed systemic CD8 [+] T-cell depletion and splenic/axial marrow sequestration in advanced lung cancer. During anti-PD-1 therapy, CD8 [+] T cells redistribute on the basis of PD-L1 status. Baseline intratumoral CD8 [+] T-cell density and early on-treatment SUVmax reduction are robust imaging biomarkers of response, outperforming peripheral blood monitoring.

Osteosclerosis refers to an abnormal increase in bone density resulting from excessive bone formation and/or reduced bone resorption. We present a case of a 31-year-old woman with acute-on-chronic abdominal pain, flushing, and diarrhea. Diffuse, mottled sclerosis involving the entire axial and appendicular skeleton was incidentally identified on imaging. Diagnostic investigations for osteosclerosis revealed a raised tryptase, leading to a bone marrow and trephine analysis. This demonstrated abnormally spindle-shaped mast cells, more than 15 in a group, with positive staining for tryptase which was consistent with systemic mastocytosis (SM). In the absence of "C" findings, a diagnosis of indolent SM complicated by diffuse osteosclerosis was made. Treatment with a histamine type-2 receptor antagonist provided mild symptomatic relief. In this report, we discuss the differential causes of osteosclerosis and the pathogenesis of bone manifestations related to SM, along with subtype-specific SM treatment options.