Introduction

The introduction of a new treatment strategy — immunotherapy — based on fighting the neoplasm by activation of the immune system, has contributed to a considerable prolongation of overall survival of cancer patients [1–4]. The drugs which activate the immune system are generally immune checkpoint inhibitors (ICIs,), which include monoclonal anti-CTLA-4 (anti-cytotoxic T lymphocyte antigen-4) and anti-PD-1/L1 (anti-programmed cell death 1/ligand 1) antibodies. Currently, the following ICIs have been registered by the American Food and Drug Administration (FDA) and/or the European Medicines Agency (EMEA): anti-CTLA-4 (ipilimumab), anti-PD-1 (nivolumab, pembrolizumab, cemiplimab), and anty-PD-L1 (atezolizumab, avelumab, durvalumab) [4].

There is a problem with the occurrence of specific toxicities associated with the use of immunotherapy — the so-called immune-related adverse events (irAE), which in some cases can be very serious or even lead to death. It should also be pointed out that currently ICIs are more and more frequently used together with other drugs, for example, chemotherapy (lung cancer), targeted therapy (kidney cancer) or as combination therapy (melanoma, lung cancer) [5], which may increase the risk of occurrence and intensification of adverse effects. Therefore appropriate qualification of patients for immunotherapy and appropriate monitoring are of paramount importance. Continuous education of medical personnel and patients and their family (caregivers) is also indicated.

This article presents the joint statement of scientific associations (Polish Oncological Society, Polish Lung Cancer Group, Polish Society of Lung Diseases, Polish Society of Gastroenterology, Polish Society of Endocrinology, and the Polish Society of Cardiology) defining the minimal diagnostic requirements (laboratory and imaging parameters) in diagnosing, monitoring, and treatment of the most common adverse events of immunotherapy in patients with malignant neoplasms.

Recommended procedure before and during immunotherapy with ICIs

A detailed medical history and appropriate additional tests before and during immunotherapy are the most important for patient safety during treatment with immune checkpoint inhibitors. It should be noted that irAEs can affect practically any organ and occur at various stages of treatment (frequently even after immunotherapy is completed) [6–11]. The mechanisms through which immunotherapy exerts its antineoplastic activity are also responsible for irAE development. These are, namely, activated T lymphocytes escaping from central control because of the inhibition of immune checkpoints, which unfortunately may lead to uncontrolled irAE development. It is particularly important to note that initially mild symptoms may in a short time intensify considerably and lead to a severe course of irAEs. Therefore, it is extremely important to perform appropriate analyses before immunotherapy and to monitor patients during treatment. The recommended procedure and analyses before and during immunotherapy are presented in Table 1.

The next aspect is the need for continuous education of patients and their family (caregivers) about the possibility of occurrence and the course of irAEs. A good clinical practice should be providing patients with appropriate materials with information (e.g. informative brochures, reference charts) about irAEs and about procedures in the case of their appearance. Patients should also be informed about using appropriate contraception when ICIs are administered, and the problems of procreation should always be discussed before initiating treatment.

There are few data on the use of ICIs in patients with pre-existing autoimmune diseases, because in most cases they were excluded from clinical trials due to concerns that autoimmune diseases may increase the risk of severe irAEs. However, an analysis of the literature data on the use of ICI in patients with pre-existing disease indicates no increase in the incidence of new irAEs, but unfortunately exacerbation of pre-existing autoimmune disease [12]. Due to the high probability of autoimmune disease exacerbation, clinical decisions regarding the use of ICI in patients with ongoing autoimmune disease should be carefully analyzed and the benefits of ICI therapy should outweigh the possible consequences of autoimmune disease exacerbation.

Immne releted adverse events associated with the gastrointestinal tract

Gastrointestinal irAEs are most common during treatment with immune checkpoint inhibitors (anti-CTLA-4, anti-PD-1, anti-PD-L1) and in some cases can be severe and even fatal. Therefore before startingimmunotherapy, a medical historyshould be collected about diseases of the gastrointestinal tract and also the motor activity of the alimentary canal (frequency of defecation, consistency of stool), to determine if after initiation of treatment an actual change has occurred and the number of defecations has increased [13–19].

It is extremely important to collect information concerning the following diseases:

In the case of coexistence of ulcerative colitis, Leśniowski-Crohn disease, or autoimmune colitis, the risk of exacerbation of these diseases during immunotherapy should be taken into consideration, as well as the increased risk of irAEs.

Diarrhea and colitis

Diarrhea can be an indication of developing colitis or other serious and potentially life-threatening immunological toxicities. Diarrhea requires strict monitoring as it can lead in a very short time to significant dehydration, and as a consequence of water and electrolyteimbalance, to acute renal failure and death.

Diarrhea is among the most frequent immunological toxicities as well as one of the main symptoms of developing immune-mediated colitis. The remaining symptoms indicating colitis are predominantly abdominal pain and the presence of blood in the stool, weight loss, fever, nausea, and/or vomiting. Immune-mediated colitis may lead to many complications, including bowel perforation, anemia, necrosis, bleeding, and megacolon toxicum.

The following should be excluded in a differential diagnosis of diarrhea and toxicity:

The examination of choice confirming the diagnosis of immunological colitis is colonoscopy with collection of samples for histopathology. The diagnosis of immunological colitis (without diarrhea) is generally based on histopathological analysis.

The differential diagnosis of grade 1 diarrhea or colitis should include complete blood count (CBC) with differential, hepatic and renal tests, electrolytes, and glucose. Additional analyses should be performed in patients with diarrhea and symptoms of colitis if they are ≥ G2 [20] and should comprise stool analysis (C. difficile), evaluation of calprotectin in the stool, or other examinations aimed at determining infection, including COVID-19 depending on the clinical indications. Determining thyroid stimulating hormone (TSH) and diagnosis of celiac disease (antibodies against transglutaminase together with total IgA concentration) is recommended if there is a clinical suspicion of celiac disease due to ICIs [13–19]. Disease progression or neoplasm dissemination in the abdominal cavity should also be excluded (in melanoma patients, metastases to the alimentary tract are common).

In cases of pronounced diarrhea or symptoms of colitis of grade ≥ 3 (G3/G4) or their long-term (≥ 5 days) persistence at grade 2 (G2), as well as in the case of doubts about the diagnosis of immunological toxicity, endoscopic analysis of the colon should be performed (sigmoidoscopy and/or colonoscopy), with taking sections for histopathological analysis [13–19]. In cases in which colonoscopy is ruled out, for instance, with suspicion of colon perforation or megacolon toxicum, computed tomography (CT), which is an effective and non-invasive option, should be performed. Irregularities in the CT picture associated with immunotherapy-induced colitis include mesenteric swelling and thickening of the colon wall.

Recommended additional analyses in patients with suspected/diagnosed diarrhea and/or immun-mediated colitis are presented in Table 2.

Hepatitis

Hepatitis associated with immune checkpoint therapy is generally asymptomatic and diagnosed by elevated serum alanine aminotransferase (ALT) and/or aspartate transaminase (AST). It should be noted that elevated levels of ALT/AST may also be associated with muscle damage, including the cardiac muscle; therefore, an extension of the diagnosis in this direction is recommended (creatine kinase levels, troponin, ECG, etc.).

In a differential diagnosis, the following factors should also be taken into consideration: the appearance or progression of metastases to the liver, cholestatic jaundice, infections [including hepatitis type B or C virus, CMV, Epstein-Barr virus (EBV), sepsis], hepatic vein thrombosis, diet (including alcohol consumption), use of other drugs, stimulants, or supplements (alternative medicine) by the patient, other autoimmunological diseases, and genetic background or coexisting diseases. Laboratory analyses evaluating hepatic function should be performed before each immunotherapy infusion.

Diagnostic analyses at the moment of the occurrence of grade ≥ 2 toxicity should include ALT, AST, alkaline phosphatase, clotting estimation — prothrombin time/international normalized ratio (INR), bilirubin levels in serum, iron levels, autoimmunological panel for hepatitis: anti-nuclear antibodies (ANA), anti-neutrophil cytoplasmic antibodies (ANCA), anti-mitochondrial antibodies (AMA), peripheral ANCA (p-ANCA), anti-smooth muscle antibodies (ASMA), and analyses for hepatitis C virus (HCV), hepatitis B virus (HBV), and CMV, EBV [13–19].

In the case of hepatic toxicity of grade ≥ 3, abdominal imaging tests should be considered [e.g. computed tomography, magnetic resonance imaging (MRI), etc.] if the patient had prior liver disease or there is a suspicion of progression of the disease/metastasis to the liver.

A biopsy may be considered to determine the cause of unsuccessful therapy with steroids or suspicion of steroid-resistant immunological hepatitis [13–19].

Laboratory analyses [ALT, ASP, alkaline phosphatase (ALP), gamma-glutamyl transpeptidase (GGTP), bilirubin, albumins, PT/INR] should be repeated once a week in the case of G1–G2 liver toxicity and every 1–2 days at toxicity ≥ G3.

Indicated additional examinations in patients with suspected/diagnosed autoimmune hepatitis are presented in Table 3.

Immune related adverse events associated with the endocrine system

Immune-related adverse events are relatively common in the endocrine system and it is important to note that in many cases they will persist after immunotherapy is completed. Usually it is associated with permanent damage to the endocrine gland or impaired function as a result of autoimmune reactions. The most common endocrinopathies are hypothyroidism or hyperthyroidism and hypophysitis. The damage rarely concerns multiple endocrine organs, however, this may make both the diagnosis and the treatment difficult, as hypophysitis, thyroiditis, or adrenalitis due to immunotherapy often give unspecific symptoms such as, for example, nausea and vomiting, headache, fatigue, or perturbed vision. It is also difficult to estimate the frequency of endocrinopathy occurrence because of different methods of evaluation, diagnosis, and monitoring in clinical trials. Symptoms that may suggest the development of endocrinological immunological toxicities are presented in Table 4.

Hyperthyroidism/hypothyroidism

Thyroid function perturbations in the course of immunotherapy are the most common immunological complication concerning the endocrine system. They may take the form of hyperthyroidism or hypothyroidism, and in some cases the initial hyperthyroidism transforms into hypothyroidism. In most patients both hypothyroidism and hyperthyroidism are asymptomatic or show equivocal symptoms, requiring routine monitoring of biochemical blood parameters such as TSH, free triiodothyronine (fT3), and free thyroxine (fT4). Thyroid function (TSH, fT4) should be examined every 4–6 weeks during ICI treatment and continued every 6–12 months after termination of treatment.

Hypophysitis

Hypophysitis is a serious AE associated with immunotherapy as it may lead to considerable hormonal perturbations, including: secondary adrenal insufficiency caused by ACTH (adrenocorticotropic hormone) deficiency (adrenocortical insufficiency may require immediate medical attention), secondary hypothyroidism due to TSH deficiency or disorders due to follicle-stimulating hormone (FSH) and luteinizing hormone (LH) deficiency.

The most common hypophysitis symptoms are fatigue, nausea, vomiting, weakness, headaches, blurred vision, and perturbations of sexual functions (including loss of libido or menstrual disorders, or erection perturbations). Hypophysitis is diagnosed by analyzing concentrations of hormones produced by the hypophysis: low concentrations of ACTH, TSH, FSH, LH, growth hormone (GH), and prolactin, and by imaging studies, including MRI. MRI (preferably performed according to the pituitary protocol) may confirm immunological hypophysitis and exclude other causes of perturbations of the hypophysis, including metastases. Moreover, it should be noted that the results of assaying cortisol and ACTH may be perturbed if patients receive steroids at the beginning of treatment, for example, patients with lung cancer simultaneously receiving chemotherapy and checkpoint inhibitors with dexamethasone premedication.

Primary adrenal insufficiency

Adrenal insufficiency is rare during ICIs treatment. However, this is an emergency that requires prompt intervention. It may cause dehydration, hypotension and electrolyte imbalance (hyperkalaemia, hyponatraemia) up to an adrenal crisis. Intravenous corticosteroids and immediate hospitalization are recommended when an adrenal crisis is suspected.

Type I diabetes

Checkpoint inhibitor treatment is associated with an acute start of type I diabetes in about 0.2–0.9% of cases. Unfortunately, in many cases, patients have severe hyperglycemia or even ketoacidosis. However, some patients are asymptomatic, and some have symptoms such as fatigue, nausea, weight loss, polyuria, or polydipsia. All cases require insulin treatment from the moment of diagnosis and in general permanent insulin supplementation. Diabetes associated with ICI treatment may develop immediately after its initiation but also even a year later. Thus it is extremely important to monitor glucose concentrations at each dose of immunotherapy.

Indicated additional tests in patients diagnosed with/suspected of immunological complications associated with the endocrine system are presented in Table 5.

Immune related advers events associated with the respiratory system

Diagnosis of immune related pneumonitis (IP) is not easy. Both clinical and radiological symptoms are not characteristic and require differentiation from infectious pneumonia, progression of neoplastic disease, or pneumonitis due to radiotherapy. During periods of increased infections with the SARS-CoV-2 virus, differentiation between IP and COVID-19 with pneumonia may be problematic because of the similarity of clinical and radiological symptoms [21].

The symptom most commonly reported by the patients is dyspnea and coughing, less commonly other symptoms such as fever, pain, discomfort in the chest, tachycardia, a sensation of cardiac palpitations, or fatigue [22].

Over one-half of IP patients also have toxicity symptoms from other organs [23]. Importantly, IP is asymptomatic in one-third of the patients [23].

A preliminary imaging study is a chest X-ray that shows new pathological changes in the pulmonary parenchyma but does not allow the determination of their exact character. Radiological monitoring of the response to treatment using chest radiograms seems justified, especially in patients with a good general status or achieving a rapid clinical improvement, as it is an easily accessible analysis, it is cheap and is not a burden for the patient.

The basic radiological analysis in diagnosing IP is spiral chest CT with contrast. This allows evaluation of the character of the changes in lung parenchyma and the lymph node appearance and, therefore, is useful for differential diagnosis between IP and other possible causes of pathology mentioned above. IP appearance in a chest CT is not characteristic and most commonly has the form of consolidation and frosted glass but also it can look like organizing pneumonia, different interstitial lesions (thickening of interlobular septa, infiltration around bronchovascular bundles, subpleural reticular, and honeycomb lesions), pneumonitis with hypersensitivity with intralobular tumors, peribronchiolar infiltration, a tree with buds, or a combination of the above-mentioned images [22, 23]. If CT is the selected method of monitoring the response to treatment, a complementary method may be the use of high-resolution computed tomography, enabling a better, as compared to standard CT, evaluation of the character and intensity of interstitial lesions in patients with persistent radiological changes [24].

Laboratory analyses are helpful in differential diagnosis of other coexisting organ toxicities of immunotherapy. Immunological pneumonitis is associated with a moderate increase in C-reactive protein (CRP) concentration, and a decrease in CRP concentration correlates with response to treatment [25]. Therefore, additional laboratory tests (e.g., determining procalcitonin concentrations in serum) or bacteriological and virological analyses may be necessary to differentiate IP and pneumonia caused by an infectious agent.

In selected situations, bronchofiberoscopy with collection of biological material and/or bronchoalveolar lavage (BAL) are indicated. The BAL results from patients with IP are characterized by a higher percentage of lymphocytes [26]. Bronchoalveolar lavage may be used for bacteriological and mycological cultures and to check for infection with Pneumocystis jiroveci. An alternative material from the lower respiratory tract which is easier to obtain is sputum — a positive culture result indicates an infectious etiology.

In particular cases, bronchofiberoscopy also allows collection of tissue material through transbronchial biopsy of suspicious radiological lesions. Histopathological analysis will allow the diagnosis of the type of pneumonitis (organizing pneumonia, granulomatous pneumonia, diffuse vesicular damage, or eosinophilic pneumonia) [27].

Functional lung tests, i.e., spirometry with evaluation of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) and diffusing capacity of the lung for carbon monoxide (DLco), should be performed in patients with established changes in the lung parenchyma. In patients with suspected perturbations of a restrictive type evidenced by spirometry, body plethysmography should be performed to detect lung parenchyma restrictions. Additional tests in patients with suspected/diagnosed immunological pneumonitis are presented in Table 6.

Immunological complications related to the cardiovascular system

Immunological complications associated with the cardiovascular system are observed relatively rarely in the course of immunotherapy, but their consequences can be very serious, and in some cases, they may even lead to death. However, due to the high effectiveness of immunotherapy in treating patients with neoplasms, treatment should not be stopped without clear clinical evidence of the possibility of developing cardiac toxicity during immunotherapy as this could considerably worsen the patient’s prognosis. Therefore, patients treated by immunotherapy should be under special cardiological supervision [28, 29].

The analysis of available trials indicates that the potentially increased risk of complications during immunotherapy is associated with the neoplasm, its prior or concomitant treatment, the status of the immune and cardiovascular systems, and most probably with genetic factors. Potential risk factors promoting higher frequency of adverse events during immunotherapy are presented in Table 7.

For cardiological supervision during immunotherapy, a preliminary evaluation is important which should include a detailed cardiological interview, measurement of basic heart functions (echocardiography — ECG), determination of basic biochemical parameters including cardiac troponins and N-terminal pro-B-type natriuretic peptide (NT-proBNP). The cardiac irregularities/diseases observed during the primary check-up should be clinically corrected or stabilized before initiating immunotherapy [30].

In supervising patients who are receiving immunotherapy, ECG, NT-proBNP, and cardiac troponin assays appear to be broadly accessible, most useful, and at the same time easy and least cumbersome. These are preliminary assays; if irregularities are observed in their values or clinical doubts arise, their broadening is indicated. It is very important to not only diagnose irregularities but also to compare them with the initial results (dynamics of changes), which facilitates therapeutic decisions. Determining cardiac troponin seems to be of particular importance, as it is a simple and specific marker of cardiac muscle [30–35]. Additional analyses in patients with suspected/diagnosed immunological toxicities concerning the cardiovascular system are presented in Table 8.

Conflict of interest

T.K.: fees for lectures from BMS, Gilead, Roche, MSD, AstraZeneca. Did not affect the content of this article.

B.C-S: fees for lectures from MSD, BMS, Pierre Fabre, Novartis, and grants for participation in meetings from MSD, Pierre Fabre, Novartis. Did not affect the content of this article.

P.L.: fees for lectures from AstraZeneca, Bausch Health, Bayer, Boehringer Ingelheim, Gedeon Richter, Merck, MSD, Novartis, Pfizer, Polpharma, Roche, Roche Diagnostic, Servier, Zentiva. Did not affect the content of this article.

P.R.: fees for lectures and Advisory Boards from MSD, BMS, Merck, Sanofi, Pierre Fabre, Blueprint Medicines, Philogen, AstraZeneca. Did not affect the content of this article.

B.K-K.: consulting for Merck, IPSA, Ipsen, Novartis, Pfizer, fees from Merck, IPSA, Ipsen, Novartis, Pfizer. Did not affect the content of this article.

The other authors have no conflicts of interest to report.

References