For mediastinal disorders, invasive biopsy is an important diagnostic step that provides tissues for pathological and molecular evaluations. Historically, mediastinoscopy or thoracoscopy used to be considered the reference standard technique for obtaining mediastinal materials, yet endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA), with its super safety profile and promising diagnostic ability has recently revolutionized this field and has become the mainstream approach.1,2 Although serving as the preferred initial tool for mediastinal staging of patients with lung cancer, one of the innate limitations of EBUS-TBNA is the restricted availability of intact tissue obtained by needle puncture, which usually suits for a cytological but not histopathological diagnostic workup, and thus might give suboptimal yields specifically in lesions of non-lung cancer aetiologies that are often more challenging to diagnose.3-5 To circumvent these limitations, other mediastinal biopsy techniques based on minimally invasive procedures have been proposed for higher accuracy. Forceps biopsy performed under real-time EBUS guidance, a relatively new technique to extract more mediastinal tissue, shows augmented sample quality and consequently improved diagnostic yield, especially in sarcoidosis and lymphoma.6

Transbronchial biopsy with a cryoprobe has been introduced over the past decade and is typically used for pulmonary parenchyma sampling in interstitial lung disease.7 This approach has proven superior to forceps biopsy in overall diagnostic yield as it provides for additional relevant pathological information due to larger samples of lung tissue without crushing artifacts.8,9 Inspired by the successful implementation of cryoprobes in the collection of lung tissue, we were the first to show that transbronchial mediastinal cryobiopsy with EBUS guidance is an equally safe while more efficient approach for the acquisition of diagnostic tissues compared to needle sampling, particularly for uncommon tumours and benign disorders.10,11 Moreover, we and other groups have previously demonstrated that both forceps biopsy and cryobiopsy offer additional diagnostic benefits to EBUS-TBNA.12,13 However, it has yet to be determined which of these two emerging techniques is more compatible with conventional needle strategy in terms of added diagnostic gain relative to added risk. Hence, the present study prospectively evaluated the added value of transbronchial mediastinal cryobiopsy versus forceps biopsy as an adjunctive approach to standard EBUS-TBNA for the diagnosis of mediastinal diseases, with diagnostic yield and procedure-related adverse events as the primary outcomes.

For the details of the study protocol please see Supplement.

In this prospective, dual-centre, randomised clinical trial, we determined the clinical value of transbronchial forceps biopsy and mediastinal cryobiopsy in addition to standard needle biopsy for the diagnosis of mediastinal lesions and perihilar lymphadenopathy. Our data show a significant increase in diagnostic yield by the combination of EBUS-TBNA with either forceps biopsy or cryobiopsy. No significant difference in diagnostic yield was detected between the two combinations. Yet, additional cryobiopsy is less time-consuming, and provides for larger specimens that are better suited for lung cancer molecular genetic analysis and immunological profiling. Direct comparison of the two adjunct approaches yielded a higher overall sensitivity of cryobiopsy alone for mediastinal diseases.

Guidelines recommend EBUS-TBNA as the method of choice for accessing the mediastinum, and especially for the detection of lung cancer metastases.3,16 Yet, endoscopy-guided needle aspiration is limited by the small amount of retrieved material that in many cases can only be used for cytologic evaluation, making the diagnosis of mediastinal lesions from non-lung cancer causes challenging.17,18 Given the revolution of lung cancer management that has shifted from empirical chemotherapy to a personalized approach, alternative ways capable of harvesting sufficient high-quality materials enabling molecular and immunological information have attracted evolving interests. In an attempt to improve the acquisition of histological tissue from mediastinal lymphadenopathies, EBUS-guided forceps biopsy has recently been developed. Several studies have demonstrated its improved diagnostic yields for sarcoidosis and lymphoma.6,13,19 Yet, the largest prospective study of mediastinal forceps biopsy so far suggested in fact a lower sensitivity for the detection of malignancies as compared to standard EBUS-TBNA.14 Motivated by the potential of cryobiopsy to produce sizeable and well-preserved lung specimens, we recently used the cryoprobe as a novel sampling technique for the diagnosis of mediastinal disease.10,11,20,21 In our prior clinical studies, cryoprobe proved superior to standard needle aspiration, in part due to its capacity to obtain sufficient tissue samples for detailed histopathological assessment.11

Of late, there is a rising interest in combined application of needle aspiration and either forceps biopsy or cryobiopsy, aiming at synergistic accuracy.12,22 However, despite a substantial and rapidly expanding body of literature, two critical questions have so far remained unanswered: a) which of these two techniques, forceps or cryobiopsy, may yield the higher diagnostic accuracy either alone or in combination with EBUS-TBNA, and b) which technique is better suited for needle biopsy?

In the past, we have been among the pioneers in the use of forceps biopsy and cryobiopsy for endobronchial and peripheral pulmonary lesion sampling, indicating an overall superiority of cryobiopsy over forceps biopsy for establishing a diagnosis, in part due to higher sample volumes and better sample quality.23-25 To directly compare the usefulness of forceps versus cryobiopsy for the diagnosis of mediastinal lesions, we initiated this prospective study. The exceptional performance of cryosampling in view of its ability to provide the largest mediastinal tissue samples among the minimally invasive endoscopic techniques translated into a superior overall diagnostic yield. Particularly, cryobiopsy enhances accuracy in the detection of mediastinal metastases, and produces samples more conducive to lung cancer molecular testings, which is consistent with prior observations reported in the literature.14,26,27 Technical difficulties have previously been proposed as reasons for the relatively inferior performance of forceps biopsies, such as acute angles of forceps penetration or a fibrotic mediastinum.14 However, taking into account the adequate samples harvested by forceps in our study, we consider its inferiority in mediastinal metastases might primarily be the result of the small tissue size and crush artifacts, which subsequently narrows the scope of sampling and dampens specimen quality. Cryobiopsy, on the other hand, provides for a greater quantity of intact tissue without crush artifacts, and may thus overcome the problem of lesion heterogeneity within metastatic lymph nodes, consequently minimizing the likelihood of a false negative diagnosis. Likewise, a better diagnostic yield for rare tumors and benign disorders was shown for cryobiopsies, although this difference was not statistically significant.

Consistent with previous studies, both forceps biopsy and cryobiopsy increased the overall diagnostic yield of needle aspiration when used as complementary techniques in addition to EBUS-TBNA.12,13 In contrast to the superior efficacy of cryobiopsy in the head to head analyses, the added values of these two combined strategies did not differ significantly. Yet, the amount of material obtained from one cryobiopsy exceeded that from three biopsies with large forceps, while demanding less procedural time. In addition, lung cancer patients may benefit from combined needle aspiration and cryobiopsy due to the increased suitability of the obtained tissue for molecular testings. In line with our prior report, EBUS-guided biopsies were generally safe, with minor bleeding as the most frequently encountered complication.28 No cases of pneumomediastinum, serious bleeding, mediastinal infection, or perioperative death were observed. Post-procedural pneumothorax occurred in 1.5 % of participants with no clinical symptoms, and was self-resolving with no need for drainage. The study design precludes a definitive attribution of these adverse events solely to needle aspiration or its supplementation.

The present study has several limitations. First, because of initial safety concerns, we opted to biopsy only the most suspicious lesion, and it is therefore possible that the utility of these sampling methodologies could thus be impaired. Indeed, the overall diagnostic yields observed in this study are slightly lower than those reported in literature. Nevertheless, the discrepancy might be primarily ascribed to the large proportion of non-lung cancer cases in our cohort, and the strict criteria that the plausible benign diagnoses were judged as negative (nearly one tenth of the cohort). Second, a 1.5- rather than a 1.9 mm biopsy forceps was applied in this trial, due to the challenge of passing the latter through the bronchoscopy's working channel, which may limit the sample volume that can be retrieved by the forceps. Recent studies, however, indicate that the diagnostic accuracy of these two different forceps sizes is comparable.29,30 Finally, on-site cytology was not routinely performed in order to avoid bias in diagnostic analyses. Yet, EBUS procedures followed current guidelines, suggesting no significant influence of ROSE on diagnostic accuracy.31

We here report the first prospective trial to evaluate the use of forceps versus cryoprobe for the diagnosis of mediastinal lesions. In comparison with forceps biopsy, substantially larger tissue samples can be obtained by bronchoscopic cryosampling within shorter time, indicating enhanced effectiveness. In direct head-to-head comparison, cryobiopsy was superior to forceps biopsy in overall diagnostic yield, yet this difference was no longer significant when both techniques were used as add-on to needle aspiration. Needle aspiration supplemented by cryobiopsy remained, however, superior for lung cancer molecular testings compared to the combination of EBUS-TBNA and forceps biopsy. As such, transbronchial mediastinal cryobiopsy might be a valuable adjunct to conventional needle-based biopsy.