Lung cancer is the leading cause of cancer-related mortality worldwide [1]. As a result of the National Lung Screening Trial (NLST), screening using low-dose computed tomography (CT) in high-risk groups aged 55 to 74 with a 30 pack-year or more smoking history reduced the mortality rate from lung cancer by 20% [2]. In addition, the United States Preventive Task Force (USPSTF) recommends annual screening for lung cancer with low-dose CT in adults aged 50 to 80 years who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years, according to the results of the Nelson Trial [3,4]. Accordingly, incidental pulmonary nodules are increasing [5,6].

The National Comprehensive Cancer Network (NCCN) guidelines suggest that biopsy should be considered if an incidentally discovered pulmonary nodule is larger than 8 mm and the patient belongs to a high-risk group for lung cancer [7]. Pathological examination through biopsy can also determine whether a patient has primary lung cancer or metastatic cancer, and classify the histologic subtype of lung cancer. A sufficient amount of tissue is required to predict the therapeutic response to driver mutations or immune checkpoint inhibitors [7].

Transbronchial lung biopsy with radial endobronchial ultrasound (rEBUS-TBLB) and CT-guided transthoracic needle biopsy (CT-TTNB) are two commonly used methods to investigate peripheral lung nodules. According to a meta-analysis of randomized controlled trials, CT-TTNB had a higher diagnostic yield than rEBUS-TBLB (83.45% vs. 68.82%; risk difference, -0.15; 95% confidence interval [CI], -0.24 to -0.05) especially for lesion size 1 to 2 cm (83% vs. 50%; risk difference, -0.33; 95% CI, -0.51 to -0.14). However, rEBUS-TBLB was found to have a significantly better safety profile with lower risks of pneumothorax (2.87% vs. 21.43%; odds ratio [OR], 0.12; 95% CI, 0.05 to 0.32) and combined outcomes of hospital admission, hemorrhage, and pneumothorax (8.62% vs. 31.81%; OR, 0.21; 95% CI, 0.11 to 0.40) [8].

Recently, new techniques, such as robotic-assisted bronchoscopy (RAB), have been introduced to complement the diagnostic yield of rEBUS-TBLB [9]. Additionally, studies have been published on improving diagnostic yield using cryobiopsy, along with conventional biopsy devices [10-12]. In this review, we describe both widely used, and newly introduced, advanced bronchoscopy techniques.

The rEBUS-TBLB uses a miniature ultrasound probe (rEBUS probe) that emits ultrasound waves that are reflected by the tissue, creating a 360° real-time image of the airway and the surrounding lung tissue. This allows the physician to identify the location of the lesion, and guide the biopsy devices to the target lesion for biopsy. The rEBUS probe is inserted through the working channel of a flexible bronchoscope or catheter (guide sheath [GS]). This enables the clinician to determine the lesion’s exact location and size [13,14].

In a recent systematic review and meta-analysis that included 51 studies with a total of 7,601 subjects, the pooled sensitivity of rEBUS-TBLB was 0.72 (95% CI, 0.70 to 0.75), and the area under the receiver operating characteristic (ROC) curve was 0.96 (95% CI, 0.94 to 0.97), while the pneumothorax incidence rate was only 0.7% (95% CI, 0.3 to 1.1) [15].

Electromagnetic navigation bronchoscopy (ENB) is a medical procedure that utilizes electromagnetic technology to localize and guide endoscopic tools or catheters. The magnetic field and generator create a low-intensity electromagnetic field around the patient’s chest, which allows the location sensor at the tip of the guide catheter to be tracked in real time. The computer software uses the sensor data to display the position of the catheter on a three-dimensional (3D) bronchial map, which helps the physician navigate to the target lesion [23].

In 2004, the Medtronic superDimension/Bronchus system, also known as the inReach system (superDimension Ltd., Herzliya, Israel), was approved by the Food and Drug Administration (FDA). Using electromagnetic guidance to manage peripheral lung lesions, this system is a minimally invasive image-guidance localization and navigation system.

The NAVIGATE study, a large, multicenter cohort study including 1,215 consecutive subjects from 29 sites, showed a diagnostic yield of 73% at 1-year follow-up results. This study diagnostic yield was comparable to other studies, even though it included only 48.5% (60% to 70% in other studies) of subjects with a positive computed tomography bronchus sign (CTBS), which is known as a significant favorable factor [24-27]. In other studies, when CTBS is negative, the diagnostic yield is only 31% to 49.6%, but in the NAVIGATE study, it was reported to be 67.1% [25,28].

RAB is a procedure that uses a robotic arm to guide a flexible tube with a camera and biopsy tools into the lungs. RAB systems were designed to reach the peripheral lung airways, similar to the traditional electromagnetic navigation system, but with better stability and steerability during the biopsy. There are currently two RAB systems available: the Monarch platform (Auris Health Inc., Redwood City, CA, USA), and the ion endoluminal system (Intuitive Surgical, Sunnyvale, CA, USA). While the two systems are similar in planning the path to the target lesion using a 3D airway map reconstructed from pre-procedure thin-section chest CT images, the navigation principles are totally different.

The development of cryobiopsy technology was inspired by the Joule-Thomson principle, where rapid freezing occurs with the sudden expansion of certain gases as they move from a high-pressure to a low-pressure environment [36]. Transbronchial lung cryobiopsy (TBLC) has been widely accepted as a biopsy method for interstitial lung diseases [37]. This technique utilizes a freezing probe to collect lung tissue samples that are superior in size and quality, compared to those obtained through conventional TBLB [38]. Cryobiopsy can be used in combination with ENB or RAB, as well as conventional biopsy modalities, to improve diagnostic yield [39,40].

Recently, TBLC has been widely used in the diagnosis of PPLs. In particular, with the development of a 1.1 mm cryoprobe, it has become possible to perform cryobiopsy through a GS following conventional biopsies, such as forceps, aspiration needle, and brushing, when performing rEBUS-GS-TBLB [10-12].

It has been reported that when cryobiopsy is used in combination with the conventional biopsy methods, diagnostic yield increases. In the case of ‘adjacent to’ on rEBUS, relatively higher benefit can be obtained than in the case of ‘within.’ Several retrospective studies have reported that when cryobiopsy is performed following conventional biopsy in the ‘adjacent to’ lesions, an additional diagnostic yield of 14.5% to 29.9% can be obtained [10-12]. In addition, Matsumoto et al. [11] reported that lesions with a negative bronchus sign had a relatively high additional diagnostic yield, compared to lesions with a positive bronchus sign (15.4% vs. 6.3%, p=0.011).

When cryobiopsy is performed in the ‘adjacent to’ orientation, a high additional diagnostic yield can be obtained, because normal anatomical structures (e.g., bronchial mucosa) are removed together when obtaining the cryobiopsy specimen. Therefore, as cryobiopsy is repeatedly performed, the location where the tissue is obtained gradually moves to the center of the lesion (Figure 4) [12].

In PPLs, cryobiopsy increases the risk of bleeding, but no deaths have been reported; it is known to be relatively safe to perform by an experienced operator, even in high-bleeding-risk patients [41,42].

Endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) plays a crucial role in the staging of lung cancer, particularly in determining the extent of mediastinal lymph node involvement. The diagnostic performance of EBUS-TBNA to identify malignancy in lymph nodes had a sensitivity of 92.3%, a specificity of 100%, and a negative predictive value of 96.3% [43].

The EBUS-TBNA can also be used for pathological diagnosis in central lesions and mediastinal lesions. However, the diagnostic yield of EBUS-TBNA in certain types of mediastinal lesions can be limited, due to the inability to obtain sufficient intact tissue samples. In diagnosing mediastinal tuberculosis lymphadenitis, the sensitivity and specificity were 72.4% and 100.0% respectively. For diagnosing sarcoidosis, the sensitivity and specificity were 71.4% and 100.0% respectively [44].

Transbronchial mediastinal cryobiopsy is a biopsy method that has been introduced in recent years, and is currently being performed in several institutions. It is performed by inserting a cryoprobe into the lesion combined with EBUS-TBNA. Typically, a 1.1 mm cryoprobe is used. This can provide larger and better-quality samples than EBUS-TBNA, which might improve the diagnostic yield for certain conditions, such as uncommon tumors and benign disorders (Figure 5) [45,46].

Fan et al. [45] carried out an open-label, randomized trial across three medical facilities in Europe and Asia. The study included patients who were 15 years or older, and had at least one mediastinal lesion measuring 1 cm or more on the short axis. Participants were randomly assigned (1:1) to the combined use of EBUS-TBNA and transbronchial mediastinal cryobiopsy (combined group, n=136) or EBUS-TBNA alone (control group, n=135). When mediastinal cryobiopsy was added to the conventional EBUS-TBNA, the overall diagnostic yield increased from 81% to 93% (p=0.0039). When cryobiopsy was added in benign diseases, the diagnostic yield was significantly higher than the EBUS-TBNA alone group (34% vs. 24%, p=0.0009). However, there was no significant difference in diagnostic yield between the two groups in lung cancer and uncommon tumors [45]. Grade 3 or higher bleeding occurred in two patients (1%) and three patients (2%) in the EBUS-TBNA alone group and combined group, respectively (p=1.00), while pneumothorax occurred in four patients (3%) and two patients (1%), respectively (p=0.67).

Genomic testing for lung cancer and programmed death-ligand 1 (PD-L1) immunohistochemistry assay were applicable in nearly all (37 out of 38, 97%) of the non-small-cell lung cancer samples obtained through the combined method, while they were only feasible in 30 (79%) out of 38 samples from the EBUS-TBNA alone method (relative risk, 1.23; 95% CI, 1.04 to 1.47; p=0.033).

Therefore, to date, there is little evidence of the need for mediastinal cryobiopsy in terms of diagnostic yield for lung cancer, but when genomic testing and PD-L1 immunohistochemistry assay are necessary, it can be considered.

A meta-analysis indicates that the addition of forceps to conventional EBUS-TBNA enhances diagnostic accuracy in the tissue diagnosis of intrathoracic adenopathy. This study demonstrates a significant increase in diagnostic yield with the combined method, achieving 92% (428 out of 467 cases), compared to a 67% yield (312 out of 467 cases) when utilizing EBUS-TBNA alone. Notably, in specific pathologies, such as lymphoma and sarcoidosis, the combined approach substantially elevates diagnostic yield: 86% for lymphoma vs. 30% for EBUS-TBNA alone, and 93% for sarcoidosis, in contrast to 58% with the solitary EBUS-TBNA method [47].

Studies using 19-gauge TBNA needles were conducted to overcome the limitations of standard 21- and 22-gauge EBUS-TBNA needles, which have a small amount of core and a crushed structure. These studies revealed that while the use of a 19-gauge needle did not enhance the diagnostic yield, it facilitated the acquisition of larger tissue samples, proving more beneficial for comprehensive histopathological evaluation and molecular testing without an increase in complications [48,49]. Although the 19-gauge needle may have potential benefits in situations necessitating the assessment of cellular architecture, such as in lymphoma subtyping or in the presence of necrotic tissues, definitive evidence supporting its superiority remains inconclusive to date. Therefore, the choice of needle gauge should be contingent upon individual patient needs and the specific requirements of the diagnostic evaluation.

With the development of various advanced bronchoscopic techniques, the minimally invasive non-surgical biopsy methods have become a trend in the diagnosis and staging of lung cancer. These techniques can be used alone, or in combination. When combined with conventional biopsy tools, cryobiopsy increases diagnostic yield, and can be used together during rEBUS-GS-TBLB, ENB, RAB, and EBUS-TBNA procedures.