LDH-to-Albumin Ratio (LAR) in Solid Tumor Patients with Cytopenia: A Simple Biomarker to Predict Bone Marrow Metastasis

<b>Objectives</b>: This study evaluated the frequency of bone marrow metastasis (BMM), its associated clinical and laboratory parameters, and its effects on survival in patients with solid tumors who underwent bone marrow biopsy due to cytopenia. Furthermore, the diagnostic power of inflammatory biomarkers (LAR, NLR, PLR, HALP, and SII) in predicting BMM was systematically analyzed for the first time in a large sample. <b>Methods</b>: Data from 233 patients with solid tumors were retrospectively reviewed. Fifteen patients with therapy-related high-risk myelodysplastic syndrome and acute myeloid leukemia were excluded, leaving 218 patients included in the study. Cytopenia was categorized according to CTCAE5.0. ROC analyses were performed for the inflammatory biomarkers LAR, NLR, PLR, SII, and HALP score. <b>Results</b>: BMM was detected in 39.9% (<i>n</i> = 87) of all patients. Prostate cancer exhibited the highest incidence of BMM, while bone represented the most common site of concurrent metastasis (<i>p</i> < 0.01). Hematologic and biochemical abnormalities-including low hemoglobin, platelet, and albumin levels, along with elevated LDH-were significantly associated with BMM (<i>p</i> < 0.01 for all). Elevated inflammatory indices (LAR, PLR, and SII) also correlated with higher risk. A multivariate analysis demonstrated that LAR provided the strongest predictive value (AUC: 0.939; 95% CI: 0.901-0.955; <i>p</i> < 0.01), with an optimal cutoff of 9.21. <b>Conclusions</b>: BMM is an important condition that negatively affects survival in solid tumor patients with cytopenia. The risk of BMM especially increases in male patients and in those with high LDH and low levels of albumin, hemoglobin, and platelets. Among the evaluated inflammatory biomarkers, LAR showed the highest diagnostic performance in predicting BMM.