Microplastics and nanoplastics are ever-present environmental contaminants with inevitable exposure to humans. Recently, research evaluating the effect of micro- and nanoplastics (MNPs) on human health, and more specifically their contribution to the risk of malignancies has increased. Nonetheless, current knowledge about the effect of these particles is limited. Thus, in the present work, we are providing a thorough review of microplastic shapes, routes of exposure to humans, pathogenic mechanisms, and types of cancers proven to be associated. Importantly, there are several ways MNPs can enter the body, including, ingestion, inhalation, dermal contact, iatrogenic and medical instruments, and through the placenta during the prenatal period. The exposure causes endocrine disruption, gut epithelium impairment, gut dysbiosis, and immune system impairment and, subsequently, inflammation, cell death, genotoxicity, and gene mutations. Digestive system tract malignancies, including hepatocellular carcinoma, pancreatic, gastric, and colorectal cancers are reported to be associated with MNPs exposure as ingestion is one important way of exposure. Lung, skin, renal, and hematological malignancies, including acute myeloid leukemia (AML) and chronic lymphocytic leukemia (CML), and cancers of the reproductive system, including breast, ovarian, and prostatic are other types of malignancies. Nevertheless, knowledge of MNPs contamination effects is still limited and highly influenced by particle properties, exposure concentration, types of additives, affected tissues, and individual susceptibility. Due to the constant exposure, these particles must be considered to be an alarming issue that their effects cannot be negligible. Therefore, future research projects are encouraged to dive into the carcinogenic effects of these invisible plastic particles as the mentioned cancers are among the most prevalent types of cancers, as well.