In a patient on high-dose prednisone (40 mg/day), a PLR of 350 is largely (possibly entirely) explained by the corticosteroid effect, not by genuine immune dysregulation or cancer-related pathology. Prednisone at this dose causes: lymphopenia (ALC often falls to 0.5–1.2 × 10³/µL from baseline 1.5–3.0 × 10³/µL) due to lymphocyte redistribution to lymphoid tissues and steroid-induced lymphocyte apoptosis, and mild thrombocytosis (platelet demargination from vessel walls, typically raising count by 20–50k). Combined, this can double or triple PLR from baseline within 24–48 hours of high-dose steroid initiation. Clinical implication: do not use PLR to assess cancer prognosis, sepsis severity, or disease activity in patients actively receiving corticosteroids ≥10 mg/day prednisone equivalent. For pre-chemotherapy cancer prognostication, PLR should be measured before steroid pre-medication is given (or at least 5–7 days after stopping steroids, when the CBC differential has partially recovered). For serial monitoring in autoimmune disease, be aware that PLR changes during steroid tapers reflect drug effects as much as disease activity changes.

Not necessarily. Low PLR (<50–100) in a cancer patient can result from several scenarios that are not uniformly favorable: **1. Low platelet count (thrombocytopenia):** If platelets are low (e.g., 80k from bone marrow metastasis, chemotherapy effect, or DIC), PLR will be low regardless of lymphocyte count. Thrombocytopenia from bone marrow infiltration is actually a poor prognostic sign. Calculate PLR components separately: if platelets are low AND ALC is normal, PLR is low from thrombocytopenia — this is NOT a good prognostic sign. **2. High lymphocyte count (lymphocytosis):** If ALC is markedly elevated (e.g., >5.0k from viral infection, lymphocytic leukemia, or reactive lymphocytosis), PLR will be low. Reactive lymphocytosis from an acute viral infection is benign. Clonal lymphocytosis from CLL or lymphoma elevating ALC will lower PLR artifactually — not applicable as a cancer prognostic marker in hematologic malignancies. **3. Genuinely favorable immune status:** ALC >2.0k with normal platelets and no confounders → low PLR reflects good lymphocyte-to-platelet balance, which is genuinely favorable in solid tumor prognosis. Conclusion: Always examine the individual components (platelet count AND ALC) when interpreting low PLR, not just the ratio itself. A 'low' PLR from thrombocytopenia is NOT the same as a 'low' PLR from strong lymphocyte-mediated immunity.

There are no standardized monitoring intervals established by major oncology guidelines. PLR measurement is driven by clinical research rather than routine clinical practice guidelines at this time. For practical purposes: **Pre-treatment baseline:** Always obtain PLR before initiating chemotherapy, immunotherapy, or surgery — this is the most clinically relevant time point for prognostication. **During treatment:** Measure at each treatment cycle assessment (typically every 2–3 weeks for most chemotherapy regimens, every 3–6 weeks for immunotherapy). Since PLR is derived from a routine CBC (which is ordered at each cycle visit for blood count monitoring), PLR is automatically calculable at every visit without additional cost or tests. **For immunotherapy monitoring:** Baseline PLR (before cycle 1) and after 2–4 cycles can help predict treatment response alongside imaging. Rising PLR despite immunotherapy suggests treatment failure or immune-related adverse events. **At disease reassessment (scan timepoints):** Correlate PLR with imaging response — PLR normalization coinciding with imaging response confirms treatment effect; PLR rise despite imaging response may indicate early resistance developing. Document PLR alongside formal disease assessment parameters (tumor markers, imaging) to build a longitudinal picture of inflammatory status throughout treatment.

Yes — multiple studies across melanoma, NSCLC, bladder cancer, and colorectal cancer (MSI-H) show that elevated pre-treatment PLR independently predicts poor response to immune checkpoint inhibitor (ICI) therapy. Biological mechanism: high PLR reflects (1) elevated platelets that suppress anti-tumor T-cell responses in the tumor microenvironment by releasing TGF-β and other immunosuppressive factors, and (2) lymphopenia indicating impaired T-cell anti-tumor immunity — the very lymphocytes that ICI therapy is trying to unleash. If there are few lymphocytes and/or they are functionally suppressed, ICI therapy will have less immune substrate to activate, resulting in reduced efficacy. Reported PLR thresholds for ICI response prediction: PLR >200 in NSCLC (Xie et al., J Clin Oncol 2018); PLR >150 in urothelial carcinoma; PLR >250 in melanoma. In all studies, high baseline PLR was associated with shorter progression-free survival and overall survival. Practical implication: PLR should be included in the pre-ICI biomarker assessment panel alongside PD-L1 expression, tumor mutational burden (TMB), and tumor microsatellite instability (MSI) status. A patient with low PD-L1 + high PLR has particularly poor predicted ICI response. Conversely, a patient with high PD-L1 + low PLR has favorable predicted ICI response. This information can guide shared decision-making about ICI therapy candidacy, combination approaches, or clinical trial enrollment.