[¹⁸F]FMISO PET in Rectal Cancer: A Short Review

The World Health Organisation (WHO)predicts that the number of incidencesof colorectal cancer worldwide willrise to 1.36 million for men and 1.08 millionfor women by 2035 [1]. Hypoxia in cancer cellsleads to radioresistance [2,3]. One way toimprove personalised radiotherapy involvestargeting hypoxic regions within the tumour.Strategies to successfully identify hypoxiain rectal cancer have repeatedly failed dueto the inability to distinguish tumours withsevere or non-resolving hypoxia. Thus, it iscrucial to develop non-invasive biomarkersof tissue hypoxia in such tumours throughimaging. The invasive method of Eppendorfelectrode [4] is considered the gold standardfor measuring oxygen distribution in tumoursand has been shown to correlate with responseto RT. However, positron emission tomography(PET) is an imaging technique used to visualiseand quantify pathophysiological processes ofinterest (for example, glucose metabolism orhypoxia) within a tissue via administration ofa radiopharmaceutical (commonly known astracer). [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) is aradiopharmaceutical used to identify hypoxia invarious tumour types. Increased retention of [¹⁸F]FMISO in tumour cells is suggestive of hypoxiaand vice-versa. Therefore, the aim was to explorechanges in [18F]FMISO PET imaging parametersin human rectal tumours before and after 8-10fractions (~2 weeks) of chemoradiotherapy (CRT)to predict clinical response.