The Endoscopic Cryotherapy of Lung and Bronchial Tumors: A Systematic Review -Can We Expect a New Era of Cryotherapy in Lung Cancer?

Since the introduction of the flexible bronchoscope by Ikeda et al. [1], it has become one of the most important tools for diagnosing and treating pulmonary diseases. Its applications range from airway evaluations to interventional therapy for airway lesions. Interventional bronchoscopy using rigid and flexible bronchoscopes has progressed with the introduction of new techniques to relieve airway obstructions and bleeding control, which can be life-threatening complications of advanced lung cancer. Malignancy in the central airway may cause diverse clinical signs and symptoms depending on the location, growth rate of the obstructive lesion, diagnosis time, and involvement of surrounding structures [2,3]. The efficacy of interventional bronchoscopy for palliation of central airway obstructions has been well established, and its curative potential for early lung cancer has evolved along with current treatment modalities. The main indication for therapeutic bronchoscopy is the presence of an airway disorder resulting in a central airway obstruction to relief blockage [4]. Interventional bronchoscopy, particularly therapeutic bronchoscopy, includes many diverse modalities, such as the Nd:YAG laser, electrocautery, argon plasma coagulation, photodynamic therapy, airway stenting, brachytherapy, and cryotherapy, which all have advantages and disadvantages. Endobronchial cryotherapy, which is intended to ablate endobronchial tumors and carcinomas in situ using an ice freezing effect, was initially reported in the 1970s [5]. Although it was largely abandoned in favor of other modalities, such as laser treatment, particularly in the United States, interest in cryotherapy has continued in Europe. Endobronchial cryotherapy has been used to destroy endobronchial tumors by its cytotoxic effects of freezing tissue, thus, causing tissue death. Its clinical uses are primarily in treating patients with inoperable obstructive central lung cancers. The mechanism of local tissue destruction is applying extremely low temperatures (below -20 to -40°C). The first successful use of low temperature for treating a tumor was reported by James Arnott [6] to treat an advanced uterine carcinoma more than 150 years ago. Rigid and semi-rigid cryoprobes are used with a rigid bronchoscope, whereas a flexible cryoprobe can be used with both instruments. Cryotherapy has also been used to treat carcinoma in situ as well as benign endobronchial tumors. The advantage of endobronchial cryotherapy is that it has proven effective with minimal complications. It is also relatively easy to use and economical compared with other therapeutic modalities. Cryotherapy is safe, with no danger of bronchial wall perforation, no radiation danger, no risk of electrical accidents or fires, and does not require much special training. Patients tolerate the procedure well and show a significant improvement in symptoms. Disadvantages include delayed results and the requirement