Systemic lupus erythematosus (SLE) and lymphoma are two different diseases. However, they might mimic each other sometimes. Here, we reported a case of bone marrow infiltration as initial manifestation of large B-cell lymphoma that mimiced SLE. The patient was an elderly female whose chief complaints were edema and bilateral lower limb fatigue for one month. Initially, she was prescribed thyroid hormone supplementation and albumin infusion for hypothyroidism and hypoproteinemia, respectively. The edema was improved, but fatigue worsened and the patient was bedridden. Then further examinations revealed anemia, thrombocytopenia, elevated lactate dehydrogenase (LDH), abnormal coagulation function, positive urinary protein, reduced complement C3 and C4, and positive antinuclear antibodies. Based on the above manifestations and laboratory findings, the diagnosis of SLE was considered. After administering 40 mg/d of methylprednisolone, the patient' s edema, platelet count and LDH levels were improved, whereas her fatigue worsened to the point where she had difficulty turning in bed. When the dose of glucocorticoid tapered to 40 mg/d of prednisone, the LDH levels elevated and platelet counts decreased. The treatment response was inconsistent with SLE. In order to clarify and confirm the diagnosis, bone marrow puncture was performed and showed large B-cell lymphoma with bone marrow infiltration of 27.5% tumor cells. Enlargement of superficial lymph node or visceral organ is common clinical manifestation of lymphoma. However, our present case was bone marrow infiltration lonely without enlargement of lymph node and organ, and it is referred to as bone marrow lymphoma (BML). BML can be classified into primary bone marrow lymphoma (PBML) and secondary bone marrow lymphoma (SBML). PBML is a rare and primary tumor in the bone marrow without involvement of lymph nodes, liver, spleen and any other organs. It is easy to be misdiagnosed or missed diagnosis due to the absence of specific clinical presentation. Bone marrow examination is required and important to make the diagnosis of PBML. Diffuse large B-cell lymphoma is the most common type of PBML. SBML is caused by lymphoma in other parts of the body and invasion of bone tissue. Most of BML patients have a poor prognosis and require rapid diagnosis and treatment. The patient we reported only took two months from onset of symptoms to death. This case indicated that it was crucial to revisit the diagnostic and therapeutic strategies when treatment response was not consistent with the diagnosis.

Thymic carcinoma, thymoma, and thymic neuroendocrine tumors are rare malignancies with limited treatment options in advanced stages. Immune checkpoint inhibitors (ICIs) have shown preliminary activity in thymic tumors, although their clinical benefit and toxicity profile remain incompletely defined. We retrospectively analyzed patients with thymic tumors treated with ICIs at MD Anderson Cancer Center from 2010 to 2024. Clinical characteristics, molecular profiles, treatment details, immune-related adverse events (irAEs), and survival outcomes were collected. The primary objective was ICI safety. Secondary endpoints included objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), and overall survival (OS). Cox regression identified predictors of survival. Forty-two patients were analyzed (median age, 59 years; 55% male), comprising 29 thymic carcinomas, 8 thymomas, and 5 neuroendocrine tumors. ICIs were administered as monotherapy (55%) or combinations (45%), most commonly anti-PD-1 agents (86%). IrAEs occurred in 60% overall and in all patients with thymoma. Grade ≥3 irAEs developed in 19%, including one treatment-related death from pneumonitis. Common irAEs included fatigue, rash, and musculoskeletal symptoms. Notable neuromuscular syndromes included concurrent myasthenia gravis and myocarditis in thymoma. Among 37 RECIST-evaluable patients, ORR was 21%, and DCR was 78%. Median PFS was 6.5 months, and median OS was 9.1 months. Any-grade irAEs were associated with reduced mortality risk (HR, 0.30). TP53 mutations and lung metastases predicted worse OS, whereas CDKN2A alterations correlated with improved OS. ICIs demonstrated preliminary activity in thymic tumors but were associated with substantial toxicity, especially in thymoma. Biomarker-driven patient selection and vigilant irAE monitoring are needed.