A rare eicosanoid precursor analogue, sciadonic acid (5Z,11Z,14Z–20:3), detected in vivo in hormone positive breast cancer tissue

•Sciadonic acid, 5Z,11Z,14Z–20:3, is an arachidonic acid analogue in cells missing 6-desaturation.•For the first time, sciadonic acid is detected in human breast cancer but not in adjacent healthy tissue.•Sciadonic acid is not a substrate for prostaglandins and its substitution for arachidonic acid may affect cell-cell signaling. Numerous genetic alterations of HSA 11q13 are found frequently in several cancer types, including breast cancer (BC). The 11q13 locus harbors FADS2 encoding Δ6 desaturation which is not functional in several cancer cell lines, including hormone positive MCF7 BC cells. In vitro, the non-functional FADS2 activity unmasks 18:2n−6 elongation to 20:2n−6 and Δ5 desaturation by FADS1 to yield 5Z,11Z,14Z–20:3 (sciadonic acid) rather than 5Z,8Z,11Z,14Z–20:4 (arachidonic acid). In this pilot study we aimed to determine whether 5,11,14–20:3 appears in vivo in hormone positive human BC tissue. Fatty acids were profiled in surgically removed human breast tumor and adjacent normal tissue (n = 9). Sciadonic acid was detected in three of nine breast tumor samples and was below detect limits in normal breast tissue. The internal Δ8 double bond of arachidonic acid is required for normal eicosanoid synthesis but is missing in sciadonic acid. This pilot study demonstrates for the first time in vivo sciadonic acid in hormone positive BC tissue, warranting a larger survey study to further evaluate its appearance and the functional implications.