Altered somatosensory functioning and mechanism-based classification in breast cancer patients with persistent pain

Pain is one of the most frequent and persistent side effects of breast cancer treatment. Besides pain, breast cancer survivors (BCS) are prone to experience a myriad of other signs and symptoms related to altered somatosensory function, including for example, hypoesthesia, allodynia, and hyperalgesia, both at the local site of cancer and in remote body parts. Different breast cancer treatments can have a direct effect on somatosensory functioning, resulting in a wide range of these signs and symptoms. To our knowledge, currently no comprehensive overview exists on altered somatosensory functioning and resulting signs and symptoms in BCS with persistent pain. Investigating altered somatosensory functioning in this population could provide more insights in the underpinning pathophysiological mechanisms and consequently improve prevention and treatment in the future. Therefore, in this paper, first, normal somatosensory functioning is described. Second, quantitative sensory testing is presented as the recommend method to evaluate somatosensory functioning. Third, existing evidence on altered somatosensory functioning in BCS with persistent pain is summarized. Altered somatosensory functioning related to the most common cancer treatment modalities, including surgery and radiotherapy, hormone therapy, and chemotherapy are discussed. In addition, evidence on the presence of nociplastic pain as pain resulting from altered somatosensory functioning without evidence for nociception and/or neuropathy in BCS is summarized. At last, a discussion on this available evidence, limitations, and perspectives for clinical practice and for research are made.