The family of S100 proteins encompasses more than 20 members characterized by remarkable conformational and functional diversity. S100 proteins act as central regulators of various cellular processes, including cell survival, proliferation, differentiation, and motility. Many S100 proteins are implicated in various types of cancer as well as neurodegenerative, inflammatory, and autoimmune diseases. Recently, we have found that S100A8⁄A9 proteins are involved in amyloidogenic process in the ageing prostate, contributing to the formation of calcified corpora amylacea (CA) inclusions, which commonly accompany age-dependent prostate tissue remodelling and cancer. Amyloid formation by S100A8/A9 proteins can also be modelled in vitro. Amyloid assembly of S100A8/A9 proteins into oligomeric and fibrillar complexes is modulated by metal ions such as calcium and zinc. Here, we provide insights into the extraction procedures and review the common structural features of ex vivo and in vitro S100A8/A9 amyloids, showing that they share the same generic origin.