TK1 and lymphoma: A few reports of utilising TK1 as a biomarker of hematopoietic tumours in horses (lymphoma and multiple myeloma) were quite promising (Larsdotter et al., 2015; Moeller et al., 2020; Wang et al., 2021), but other studies showed that its performance is below expectations because false‐negative (Luethy et al., 2019; Moore et al., 2021) and false‐positive results are reported (Moeller et al., 2020).