14. Modifiable risk factors and susceptibility to COVID-19
Several modifiable risk factors may be present in cancer patients, which
can increase susceptibility to COVID-19 infection and the severity of
the disease. Common risk factors include tobacco smoking, obesity,
hypertension, and type 2 diabetes (77). Despite the known benefits of
smoking cessation even following a cancer diagnosis (78), a large
proportion of people will continue to smoke (79). Indeed, one 2017
cross-sectional study with over 26,000 individuals from the United
States identified that people diagnosed with smoking-related cancers
were more likely to continue smoking post-diagnosis than those diagnosed
with non-smoking-related cancers (80). This is a particular concern
given that ACE2 receptors are the binding site for the SARS-CoV-2 virus,
as mentioned above, and this receptor is upregulated among current
smokers (81). Moreover, it has been found that patients with any history
of smoking are vulnerable to COVID-19 infection, and are more likely to
have a severe case resulting in ICU admission, need for mechanical
ventilation, and increased mortality (82).
Although some controversy exists whereby cigarette smoking has been
associated with a lower population prevalence of COVID-19 (83), other
studies counter these findings suggesting a slight increase in diagnosis
(84). There is undoubtedly potential for nicotine to be considered as a
therapeutic modality. However, more research is required (85).
Nevertheless, the harms of cigarette smoking far outweigh any potential
therapeutic benefits associated with continued smoking for active
smokers. Therefore, encouraging smoking cessation even following cancer
diagnosis will have benefits on cancer treatment and progression and may
also reduce the risk of COVID-19 infection and severity.
Similarly, a prospective study of 92 patients from a hospital in Italy
evaluated the severity of COVID-19 and obesity classes according to Body
Mass Index (BMI), identifying an increased need for mechanical
ventilation and access to intensive or semi-intensive care units
compared to individuals classified as having normal BMIs (86).
Meanwhile, a study of 103 consecutive patients from the United States
identified that severe obesity (BMI > 35
kg/m2) was associated with more ICU admissions and
invasive mechanical ventilation (87). A 2021 systematic review and
meta-analysis compiling evidence across nine studies confirm these
findings, with severe COVID-19 patients more likely to have a higher BMI
than non-severe patients. Patients with obesity were more likely to be
severely affected by the condition and have worse disease progression
(88). Although ACE2 expression is higher in adipose tissue than lung
tissue, no current evidence suggests that COVID-19 binds directly to
adipose tissue (87). It is believed that pro-inflammatory cytokines and
adipokines, synthesized by adipose tissue, can weaken the immune
response and thus be contributing to this observed link between COVID-19
and obesity (89). It is well established that obesity causes changes in
the physiological function of adipose tissue, also leading to insulin
resistance and chronic inflammation, and these mechanisms are known to
be linked to carcinogenesis and cancer progression (90). Hence,
encouraging weight loss among people with obesity may be beneficial in
reducing the severity of SARS-CoV-2 infections.