Inhibition of tumor necrosis factor (TNF) activity has profoundly changed the management of several immune-mediated inflammatory diseases with great benefit for patients. The application of TNF inhibitors (TNFi), however, also brings a new concern, malignancy. We performed a systemic review to collect the studies reporting cancer incidences and risks in TNFi users regardless of indications. TNFi were most frequently used in treating patients with rheumatoid arthritis (RA) and inflammatory bowel diseases (IBD). In RA patients without prior cancer history, the incidences of malignancies ranged from the lowest rate 0 per 1000 person-years in etanercept users regarding lymphoma to the highest rate 35.62 per 1000 person-years in adalimumab users on non-melanoma skin cancer (NMSC), while in those patients with prior cancer history, the recurrent incidences of malignancies ranged from the lowest rate 5.05 per 1000 person-years regarding melanoma to the highest rate 63.20 per 1000 person-years on basal cell carcinoma (BCC) in TNFi users. In IBD patients, incidences ranged from 0 per 1000 person-years in TNFi users on lymphoma to 34.0 per 1000 person-years in infliximab users on overall cancer. However, these incidence rates of overall cancer, lymphoma and melanoma were not higher in comparison with those patients who were not treated with TNFi. Compared to general population, incidences of lymphoma were elevated in RA patients and rates of NMSC were higher in patients with psoriasis, RA and IBD. In conclusion, cancer incidences vary across different studies, indications, cancer types and studies with different individual TNFi. Treatment with TNFi is not associated with increased malignant risks of overall cancer, lymphoma or melanoma. Results of NMSC risk were inconsistent among studies. A latest prospective registry study demonstrated a small increased risk of squamous cell cancer in RA patients treated with TNFi (one additional case for every 1600 years of treatment experience). Further prospective studies are needed to verify whether TNFi users have higher NMSC risk than non-TNFi users.