Immune checkpoint inhibitor toxicities
Immune checkpoint inhibitors are drugs that interrupt a cancer’s ability to hijack the immune system; they block the proteins that hold back T-cells from attacking the cancer, thereby releasing the immune system to go after the malignant cells.
The two most common types of immune checkpoint inhibitors are those targeting the programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) pathways. The three currently approved PD-1 inhibitors are pembrolizumab (Keytruda), nivolumab (Opdivo), and cemiplimab (Libtayo), which can treat nearly a dozen malignancies affecting different organs. Atezolizumab (Tecentriq), avelumab (Bavencio), and durvalumab (Imfinzi) are the three currently approved PD-L1 inhibitors, indicated for urothelial carcinoma and a handful of other cancers, such as small-cell and non–small cell lung cancer and triple negative breast cancer.
The only other type of approved checkpoint inhibitor is ipilimumab (Yervoy), which targets the CTLA-4 protein. A number of other checkpoint inhibitors are in trials, however, such as ones targeting pathways involving OX40, ICOS, TIM3, and LAG-3 (J Hematol Oncol. 2018. doi: 10.1186/s13045-018-0582-8).
Immune-related adverse events are less common with PD-1 or PD-L1 inhibitors – a rate of 5%-10% – compared with adverse events from CTLA-4 inhibitors, which occur in about 15% of patients. Neurologic complications occur even more rarely – about 1%-4% of all immune checkpoint inhibitor therapies – and primarily include MG, Guillain-Barré syndrome (GBS), chronic inflammatory demyelinating polyneuropathy (CIDP), and inflammatory myositis (Muscle Nerve. 2018;58[1]:10-22).
Treatment with multiple checkpoint inhibitors increases the likelihood of severe adverse events, with rates of up to 30%-50% of patients with dual treatment.
Distinguishing features of neuromuscular immunotherapy-related adverse events
MG is the most common neuromuscular immune-related adverse event from immune checkpoint inhibitors and tends to occur 3-12 weeks after beginning treatment, frequently comorbid with inflammatory myopathy or cardiomyopathy, Dr. Trevino said. About two-thirds of cases are de novo, while the remaining one-third involve preexisting MG; no reports of Lambert-Eaton myasthenic syndrome have been linked to checkpoint inhibitors.
Several characteristics distinguish checkpoint inhibitor–associated MG from standard MG. Standard MG can be ocular with or without bulbar or appendicular weakness, whereas immunotherapy-related MG is rarely only ocular (about 18% of cases). Immunotherapy-related MG involves an MG crisis at diagnosis in up to 50% of cases and has high mortality, both of which are rarer with standard MG.
While standard MG can be seronegative or involve AChR, MuSK, or LRP4 antibodies, about two-thirds of immunotherapy-related MG cases are positive for AChR antibodies. LRP4 antibodies are rare with MG from checkpoint inhibitors, and no MuSK antibodies have been reported in these cases. Creatine kinase (CK) or troponin I (TnI) elevation occurs in about 87% of patients with checkpoint inhibitor-induced MG, but standard MG doesn’t typically involve increased CK levels.
Inflammatory myositis (IM), the second most common neuromuscular adverse event from immunotherapy, tends to occur 2-15 weeks after immune checkpoint inhibitor therapy and can involve polymyositis, necrotizing autoimmune myopathy, dermatomyositis, granulomatous myositis, or other nonspecific myositis and myopathies.
Though proximal weakness occurs with IM both associated with immunotherapy and not, ocular symptoms are unique to cases associated with therapy and occur in about half of them. Myalgia, dyspnea, and dysphagia can all occur with checkpoint inhibitor–associated IM but don’t generally occur with standard IM. Immunotherapy-related IM is usually seronegative for myositis antibodies and doesn’t generally cause abnormalities in electromyography, compared with increased exertional activity and early recruitment of myopathic motor units in electromyography with standard IM.
GBS and CIDP are the third most common cause of neuromuscular complications from checkpoint inhibitors. The main distinguishing feature of these conditions from those not related to immunotherapy is that they occur anywhere from 4 to 68 weeks after therapy begins. Presentation is otherwise similar whether related to checkpoint inhibitors or not.
Aside from GBS and CIDP, other neuropathies that can result from immunotherapy complications include acute cranial neuropathies, axonal or demyelinating neuropathies, motor polyradiculopathy, vasculitic neuropathy, and plexopathy.
Neuromuscular complications other than those described above can also occur from checkpoint inhibitor therapy, such as enteric neuropathy, polyradiculitis, and meningo-radiculo-neuritis, but these are much rarer.
Four organizations have developed consensus guidelines for immune checkpoint inhibitor toxicities: the European Society for Medical Oncology (ESMO, 2017), Society for Immunotherapy of Cancer (SITC, 2017), American Society of Clinical Oncology (ASCO, 2018), and National Comprehensive Cancer Network (NCCN, 2019).
Dr Trevino had no disclosures.