Inflammatory cytokines (interleukin-1β (IL-1β), interleukin-6 (IL-6), insulin-like growth factor (IGF-1) and tumour necrosis factor-α (TNF-α) are observed to be at a higher concentration in the peritoneal fluid of people with endometriosis [43,73,74,75]. Here, TNF is linked to endometriosis.