Validation of Differential Serum Levels for Five Minerals in South American Gallstone Patients With and Without Gallbladder Cancer

Gallbladder cancer (GBC) is a highly lethal malignant tumour characterised by a low global incidence, but with a disproportionately high prevalence among indigenous populations in the Americas. The absence of specific symptoms and validated early detection tools often leads to late diagnosis and poor prognosis. To date, no biomarkers have been established for the early detection of GBC.

Minerals and metals play a fundamental role in a wide range of biological processes, and both their excess and deficiency - in the wrong compartment or at the wrong time - can disrupt internal homeostatic balance. It has been proposed that such dysregulation is a relevant factor in carcinogenesis, operating through mechanisms including oxidative stress, DNA damage, and immune dysregulation. Although altered mineral profiles have been described in GBC, and several elements have been proposed as potential risk biomarkers, these findings remain largely exploratory and lack consistent validation in independent cohorts, particularly in populations with a high incidence of GBC.

In our previous research, we quantified the serum concentrations of more than 50 metals and minerals in 240 South American patients (120 with GBC and 120 with gallstones) from the EULAT Eradicate GBC study, of whom more than 30 met strict quality control criteria (e.g., concentrations above the lower limit of detection in at least 95% of samples). We observed that serum concentrations of aluminium (Al) and copper (Cu) were elevated, whilst those of sulphur (S), zinc (Zn) and bromine (Br) were reduced, in serum samples from patients with GBC compared with patients with gallstones.

The aim of this study is to validate the differences in the concentrations of these five minerals using an independent set of South American serum samples (n=115 patients with GBC and n=115 patients with gallstones).

Serum samples will be digested and analysed by inductively coupled plasma mass spectrometry (ICP-MS) on an Agilent 7850 instrument, using indium (In) as an internal standard for signal normalization. More than 50 minerals and metals will be quantified per sample. Based on preliminary data, it is expected that approximately 30 analytes will pass all quality filters and be retained for statistical analysis.

Metal concentration data will be analysed using R. Overall mineral/metal profiles will be assessed through principal component analysis to identify samples with atypical concentration patterns. Analytes with concentrations below the lower limit of detection in more than 5% of samples, or with a median absolute deviation not exceeding the detection threshold, will be excluded from further analyses. To validate the five previously identified associations, metal concentrations will be compared between patients with GBC and patients with gallstone disease using univariate and multiple robust logistic regression, adjusting for potential confounding factors and correcting probability values for multiple comparisons using the Bonferroni method.