A risk factor predicting when brain metastases will develop in SCLC patients is not clear. In this study, a SUAL above 6.2 mg/dL was identified as an independent factor for asymptomatic brain metastasis at diagnosis in patients with advanced SCLC. This is the first research that we know of to determine the relationship between asymptomatic brain metastasis and SUAL.

Despite the current rapid progress in molecular oncology and treatment options, platinum and etoposide are still the most important treatment strategies in small cell lung cancer [2, 3]. In recent studies, combining standard platinum and etoposide treatment regimens with immune checkpoint inhibitor monoclonal antibodies has resulted in a significant increase in treatment response and survival [2,3,4]. Although it is an aggressive type of cancer, it is clinically important that it is highly sensitive to chemotherapy and radiotherapy [2, 4]. Therefore, it is recommended that brain imaging be requested in all patients diagnosed with limited or diffuse disease, even if they are asymptomatic.

Uric acid, which is one of the end products of nucleotide metabolism, is one of the end products of nucleotide metabolism. Studies investigating the relationship between SUAL and cancer in literature focused on the proinflammatory effect of uric acid [5, 6, 15]. On the other hand, it has been stated that uric acid in high concentrations prevents lipid per-oxidation, scavenges free radicals, and may have anti-cancer effects. There are studies on the association of increased serum uric acid levels with cancer development and prognosis in a patient with cancer [16].

The studies suggest that SUAL may be an independent prognostic factor in patients with cancer is common. In recent years, there has been an increase in the number of studies attempting to show the prognostic and predictive value of SUAL in different types of cancer. It has been determined that SUAL has been investigated as a prognostic factor alone or in combination with other molecules in various cancer types. Research on lung cancer is also among these studies [17,18,19]. There are limited studies investigating the prognostic value of SUAL in SCLC. In a study by Wang et al. [19], it was determined that the tumor burden is higher, and the prognosis is poor in patients with high SUAL. On the other hand, there is no study investigating the relationship between asymptomatic brain metastasis and SUAL in small cell lung cancer.

However, in the results of the first known study investigating the prognostic value of SUAL in non-small cell lung cancer, it was reported that the rate of brain metastasis was higher and the time to brain metastasis was shorter in patients with SUAL above 7.49 mg/dL [17].

One of the main limitations of our study is the relatively low number of patients. Secondly, the fact that it is a study based on retrospective data can be considered an important limitation. Although people with gout or gout attacks were excluded from the study, the lack of data on nutritional characteristics can be considered a limitation. In particular, the fact that the patients’ alcohol and red meat consumption in the recent days before giving samples for blood tests is unknown may pose a question mark for SUAL. No anesthetic was used before and during blood collection. Considering the predictions about the effect of stress on serum uric acid levels, the fact that blood samples were taken calmly after resting in the laboratory center reserved for oncology patients where routine blood samples are taken may suggest that possible stress-related blood level changes for uric acid may have been relatively prevented. Therefore, there is a need for studies on a large number of patients in which the predictive value of SUAL can be determined by measurements made within a standard diet and timing. However, despite all these limitations, predicting brain metastasis in asymptomatic patients, regardless of stage, with an easily applicable and accessible biomarker is important for patient management.