PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s):Tumor hypoxia is known to promote radiation resistance. Tissue oxygenation and acid-base balance are intricately linked and intertwined through complex physiological pathways with oxygen-hemoglobin dynamics, pulmonary vasoconstriction, and cardiopulmonary circulation, all of which could affect oxygen delivery to the pulmonary tumor microenvironment. Although acid-base and respiratory status are ideally ascertained by arterial blood gas, venous chemistries, may be a reasonable surrogate. We hypothesized that relatively high vs low levels of serum bicarbonate (HCO3) could be associated with differential primary tumor control in NSCLC patients treated with SBRT.
Materials/Methods:We retrospectively reviewed outcomes for patients with localized NSCLC treated at our institution between 2008 and 2017. Pre-treatment serum HCO3 was recorded and obtained from the most recent basic metabolic panel (BMP) within 3 months prior to initiation of SBRT. The primary endpoint evaluated was primary tumor failure (PTF), defined as recurrence of the primary tumor. Additional secondary endpoints include overall survival (OS); regional failure (RF), defined as recurrence in regional N1-N3 nodes; and distant metastasis (DM), defined as recurrences outside of the lobe and regional nodes. Cox regression was used to test association between endpoints and pre-treatment serum HCO3, which was dichotomized as high and low by the median.
Results:A total of 117 patients and 122 treated tumors were included. Median follow up was 14.3 months. Males comprised 67.5% (79) of the cohort and females comprised 32.5% (38). Median age was 71 (range 46-92). The majority of tumors were early-stage, with 82 (67.2%) T1 and 29 (23.8%) T2 tumors. A small minority of tumors (7 (5.7%) T3 and 4 (3.3%) T4) were included due to multiple nodules thought to be from the same primary. Adenocarcinomas, squamous cell carcinomas, and undifferentiated/unspecified NSCLC represented 40.2% (49), 51.6% (63), and 8.2% (10) of the cohort, respectively. Median SBRT total dose, dose per fraction, and number of fractions was 50 Gy, 10 Gy, and 5 fractions respectively. Median HCO3 level was 27 mEq/L (range 7 to 43 mEq/L). Univariate cox regression analysis indicated lower serum HCO3 was significantly associated with primary tumor failure (HR=4.09; CI 95% 1.32-12.71, p=.015). PTF at 2 years was 4.4% (CI:1.2%-16.7%) and 24.1% (CI:13.8-40.2%) for high and low HCO3 cohorts, respectively. Median time to PTF was 10.3 and 14.1 months, respectively. There was no association between pre-treatment serum HCO3 and OS, RF, and DM.
Conclusion:Serum HCO3, as measured on a routine BMP, may be a simple, inexpensive biomarker for identifying patients at risk for PTF after treatment with SBRT. These findings necessitate validation using a large, independent cohort.
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