Impact of Histological Processing on Endogenous Elemental Contents and Distributions in Breast Cancer Tissue Sections

Abstract Trace metal homeostasis is critical for cellular function and often disrupted in diseases such as cancer. Spatially resolved techniques enable mapping of metal distributions within complex cellular environments, surpassing the limitations of bulk analyses. Formalin-fixed, paraffin-embedded (FFPE) tissues are widely used in research, yet the impact of FFPE processing on endogenous elemental contents and distributions remains unclear, with conflicting findings across sample types. This study evaluates the suitability of FFPE human breast carcinoma tissue sections for multielemental bioimaging by direct comparison with paired fresh frozen (FF) tissues and assesses potential sources of contamination or elemental losses during processing. Three FF human breast carcinoma specimens were bisected and processed as either FF or FFPE. Serial sections underwent analyses by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), alongside hematoxylin and eosin (H&E)-staining, to compare elemental profiles in whole sections and morphologically distinct regions. In parallel, FFPE processing reagents encompassing tissue-marking dyes, formalin, paraffin wax, xylene, and ethanol were analyzed via solution ICP-MS to contextualize the in situ findings. The multielemental imaging results revealed that Zn, Mn, and Fe were largely preserved in FFPE sections, supporting the continued use of such tissues for in situ metal analyses. Addition of Cu was observed for all FFPE samples, most likely caused by exposure to blue tissue-marking dye. Formalin induced variable elemental leaching, most notably affecting Mg. Paraffin wax, ethanol, and xylene contained minimal trace metal levels both before and after contact with tissues.