In a recently study, a larger number of TAMs has been observed in mice exposed with sleep fragmentation (a hallmark of sleep apnea and associated with increased tumor incidence and mortality) compared with that in mice exposed with sufficient sleep [40], at the same time, TAMs secreted from the tumor of mice with sleep fragmentation had a higher level of TLR4 expression than that from the tumor of the latter, which indicates that TLR4 signaling in macrophages may play a role in recruiting macrophages from systemic circulation to the tumor microenvironment [40] (Figure 2). Here, TLR4 is linked to sleep apnea syndrome.