MTE 19.02 Ablative Therapy for Early Stage Lung Cancer

Abstract

The fact that an early cancer is early in its nature implies that a curative therapy should be offered. However, radical treatments such as surgery and radiotherapy might not be the best options for various reasons. Firstly, the amount of normal tissue that has to be removed or denaturalized can contraindicate the treatment, secondly the unresectability for some central tumors, and finally the concern that metachronous lesions can occur and might need further intervention. Thus, the use of bronchoscopic therapies in the management of lung cancer limited to the airways has brought light to the management of early lung cancer. Several techniques are available to treat endoluminal superficial lesions, including laser, electrocautery, argon-plasma coagulation, photodynamic therapy, cryotherapy and brachytherapy. The curative potential of all these therapies has been demonstrated, as all of them are able to effectively destroy the depth of an early lung central cancer, which counts no more than 5 mm of malignant tissue. The definition of early lung cancer used in the studies of bronchoscopic therapies does not exactly correspond with the actual definitions of the TNM classification and differs among authors. Nagamoto et al. observed that squamous cell carcinoma (SCC) ≤ 3 mm thick and with longitudinal extension ˂ 20 mm was associated with no nodal involvement.1 Konaka et al. suggested that hypertrophic lesions of ˂ 1 cm are either carcinoma in-situ (CIS) or micro-invasive tumor within the muscle layer, while nodular and polypoid lesions ≥ 1 cm are more likely invasive beyond the cartilaginous layer.2 According to these, Mathur et al. defined early stage cancer as radiographically occult SCC that is endoscopically superficial, ˂ 2 cm in surface area with clearly visible margins and not invading beyond the bronchial cartilage.3 Later, the Japan Lung Cancer Society defined the bronchoscopic criteria of central type early stage lung cancer as that located subsegmental or more proximal, ˂ 2 cm with bronchoscopically recognizable margin and proven SCC.4 The new 8th edition of the TNM classification incorporates new definitions in the early stages including some special situations. Superficial spreading tumors in the central airways are those confined to the tracheal or bronchial wall regardless of size and location, and are labeled T1a ss. Carcinoma in situ (classified as Tis) now includes both squamous cell carcinoma in situ (SCIS, or squamous dysplasia) and adenocarcinoma in situ (AIS, which is localized, ≤ 3 cm and shows pure lepidic growth, lacking stromal, vascular, alveolar space or pleural invasion). Minimally invasive adenocarcinoma is classified as T1a(mi) and corresponds to solitary adenocarcinoma ≤ 3 cm with a predominantly lepidic pattern and ≤ 0.5 cm invasion. The invasive component is defined as histologic type other than lepidic or tumor cells infiltrating myofibroblastic stroma. In our setting, it is important to remark that examination of small biopsy specimens cannot exclude or quantify invasive components for AIS and T1a(mi) respectively. Although AIS can be highly suspected from biopsies with pure lepidic pattern together with a CT correlation of the ground glass component, AIS and T1a(mi) require examination of the entire resection specimen. The accuracy of the diagnostic techniques for early lung cancer represents the first step for defining the lesions suitable for endobronchial therapy. High definition bronchoscopy, autofluorescence bronchoscopy (AFB) and narrow band imaging (NBI) have been used for defining the margins of the lesion, the latter having a higher specificity. To evaluate the shallowness of the tumor, radial endobronchial ultrasound (rEBUS) and optical coherence tomography (OCT) have been used.6 Also, the combination of AFB and OCT have shown good results for both detection and characterization of premalignant lesions of the centrals airways.7 Thin-section CT (≤ 1 mm) and PET-CT might also be useful in the evaluation of premalignant lesions.8,9 Treatment success is directly dependent on lesion accessibility and the capability to correctly delineate the margins and shallowness of the lesions (10). Once the boundaries of the lesion are defined, choosing a technique over another depends mainly on the expertise of the bronchoscopist and availability of the therapy.