"High Tumor Burden" in Metastatic Non-Small Cell Lung Cancer: Defining the Concept

Identifying patient characteristics that define a worse disease prognosis or "high tumor burden" (HTB) status is essential for clinical decision-making and treatment selection in metastatic non-small cell lung cancer (mNSCLC). We aimed to define this concept based on the experience of oncologists in clinical practice. A representative sample of Spanish experts was selected and asked to complete an online survey regarding the definition of HTB according to their personal experience. HTB was identified by the oncologists (N = 81) as one of the principle factors influencing first-line treatment decision-making. According to the experts, HTB is mainly defined by the number of metastatic lesions (n = 45, 56%), location (n = 34, 42%), tumor size (sum of diameters of target lesions; n = 26, 32%) and liver involvement (n = 24, 30). High lactate dehydrogenase (LDH) levels were also associated with HTB. Almost half of respondents (n = 33, 41%) believed that one metastatic lesion was sufficient to consider a patient as presenting HTB, 72% (n = 58) considered that two were necessary and 99% (n = 80) three. Liver (n = 76, 100%) followed by brain (n = 65, 86%) were the main metastatic sites associated with HTB. Tumor size ranging from 6 cm to 10 cm as well as high LDH levels (three times the upper limit) defined the concept for 82% (n = 62) and 100% (n = 76) of oncologists, respectively. In the real-world setting, according to experts, HTB is defined by the number of metastatic lesions, location of metastases, tumor size and by high LDH levels. Given the relevance of this concept, efforts should be made to unify its definition and to further explore its potential as a prognostic factor for mNSCLC patients.