**1. Introduction**

Lung cancer remains a major problem because the number of patients is increasing worldwide, and it remains the most common cause of cancer death [1]. However, as low-dose chest computed tomography (CT) is increasingly being used for cancer screening in the general population at risk for lung cancer, the number of patients diagnosed in earlier stages who can undergo surgical treatment has increased [2]. Additionally, clinical staging [3], surgical techniques [4], and neoadjuvant and adjuvant therapies [5,6] have advanced over the last few decades. Although lung cancer treatment is still a challenge, its long-term survival rates should gradually improve with these advances, especially in early-stage lung cancers [7].

**Citation:** Kim, B.-G.; Choi, Y.S.; Shin, S.H.; Lee, K.; Um, S.-W.; Kim, H.; Cho, J.H.; Kim, H.K.; Kim, J.; Shim, Y.M.; et al. Risk Factors for the Development of Nontuberculous Mycobacteria Pulmonary Disease during Long-Term Follow-Up after Lung Cancer Surgery. *Diagnostics* **2022**, *12*, 1086. https://doi.org/ 10.3390/diagnostics12051086

Academic Editors: Monika Szturmowicz and Ewa Augustynowicz-Kopec

Received: 25 February 2022 Accepted: 25 April 2022 Published: 27 April 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

Surgical resection is the gold standard treatment for early-stage lung cancer [8]. Unfortunately, patients who develop a postoperative pulmonary complication (PPC) after the surgical resection of lung cancer experience worse long-term outcomes [9]. However, there are insufficient data on the incidence and impact of chronic complications, particularly those associated with chronic pulmonary infections. Nontuberculous mycobacteria (NTM) are ubiquitous environmental organisms that cause chronic pulmonary disease (PD), and the burdens of NTM-PD are increasing globally [10,11]. Furthermore, the incidence and prevalence of NTM-PD rapidly increased in South Korea from 2003 to 2016 [12]. Well-known risk factors for NTM-PD include an older age, underlying structural PD such as chronic obstructive lung disease (COPD), bronchiectasis, interstitial lung disease (ILD), a previous history of pulmonary tuberculosis (TB) [13,14], and the use of immunosuppressant medications [15,16].

Studies on the relationship between chronic pulmonary infection, not NTM-PD, and lung cancer surgery have been reported. Previous studies reported that lung cancer surgery is one of the risk factors for developing chronic pulmonary aspergillosis [17,18]. To the best of our knowledge, few studies have investigated the development of NTM-PD after the long-term follow-up in patients who underwent lung cancer resection surgery. Therefore, we aimed to determine the cumulative incidence of NTM-PD after lung cancer surgery and evaluate the risk factors related to the development of NTM-PD.

#### **2. Materials and Methods**

#### *2.1. Study Population and Data Collection*

This was a retrospective cohort study. We screened the medical data of patients with non-small cell lung cancers (NSCLC) who underwent lung resection surgery between January 2010 and December 2016 from the Lung Cancer Surgery Registry at Samsung Medical Center, a 1997 bed referral hospital in South Korea. Patients with a concurrent diagnosis or a previous history of NTM-PD at the time of surgery were excluded. Even when the diagnostic criteria for NTM-PD were not fully satisfied, patients with culturepositive NTM from the respiratory specimen obtained before surgery were also excluded. Additionally, patients who showed granulomatous inflammation in surgical specimens of lung cancer in which NTM infection could not be ruled out were excluded from this study.

We used the same database to gather the following information: patient-related factors, such as age, sex, body mass index (BMI), a history of smoking, underlying pulmonary diseases, other comorbidities, and CT findings at the time of the lung cancer diagnosis (TB sequelae, bronchiectasis, and centrilobular bronchiolitis); cancer-related factors, such as histologic type, location of the tumor, and the clinical/pathological stage of cancer; treatment-related factors, including the neoadjuvant or adjuvant treatments used, the surgical approach, the extent of surgical resection, and the development of any PPCs within 30 days after surgery. Underlying pulmonary diseases included a previous history of pulmonary TB, small airway disease (COPD, asthma), and ILD. The tumor was staged using the Seventh Edition of the American Joint Committee on Cancer [19]. A PPC was defined as the development of any intrathoracic complications during the patient's hospital stay or during a readmission within 30 days after surgery [20]. Patient follow-up data were last updated in February 2021.

This study obtained approval from the Institutional Review Board (IRB no. 2021- 04-016) to review and publish information from patient records, and the requirement for informed consent was waived because the patient information was de-identified and anonymized prior to the retrospective analysis.

#### *2.2. Diagnosis of NTM*

After surgical resection for NSCLC, most patients were followed-up for at least five years by a thoracic surgeon. Patients with pre-existing or newly developed pulmonary disease were jointly followed-up by a pulmonologist [17]. Physical examinations, laboratory tests, chest radiographies, and chest CT scans were regularly performed at scheduled intervals during follow-up visits. When the development of NTM-PD was suspected based

on chest CT images and pulmonary symptoms, patients were referred to a pulmonologist, and further diagnostic tests were performed as needed. The diagnosis of NTM-PD was established as follows: (i) cultured in at least two separate sputum samples or (ii) cultured in at least one or more bronchoalveolar lavage/washing specimens or (iii) lung biopsy with mycobacterial histopathologic features and positive for NTM in tissue culture or in one or more sputum or bronchial lavage fluid cultures [21]. Of course, the final diagnosis was accompanied by an appropriate exclusion of other diseases.

The diagnosis of NTM-PD usually takes months to years even in patients with suspicious clinicoradiological findings [22]. In consideration of this cohort's many deaths due to lung cancer or loss to follow-up, the following additional situations were also defined: (1) suspicious NTM-PD was defined when the microbiologic criteria were not satisfied, such as only one sputum culture-positive specimen or insufficient identification test results for NTM species; (2) NTM-positive was defined as the sum of all patients with NTM-PD and suspicious NTM-PD.

Acid-fast bacilli (AFB) smears and cultures were prepared using standard methods [23]. All specimens were cultured both on 3% Ogawa solid media (Shinyang, Seoul, South Korea) and in liquid broth media in mycobacterial growth indicator tubes (Becton, Dickinson and Co., Sparks, MD, USA). NTM species were identified using nested multiplex polymerase chain reaction and a reverse-hybridization assay of the internal transcribed spacer region (AdvanSureTM Mycobacteria GenoBlot Assay; LG Life Sciences, Seoul, Korea) [24].

The radiological classification of patients with NTM-positive results was as follows. The fibrocavitary form of NTM-PD was defined by the presence of cavitary opacities predominantly in the upper lobes. The nodular bronchiectatic (NB) type was characterized by the presence of multifocal bronchiectasis and clusters of small nodules [25]. Additionally, the NB form was divided into a "with cavity" and a "without cavity" form.

#### *2.3. Statistical Analyses*

The data are presented as a number (%) for categorical variables and as the median (interquartile range [IQR]) for continuous variables. Data were compared using the Chisquare test or Fisher's exact test for categorical variables, and the Mann–Whitney U test for continuous variables. P values for categorical variables with an ordinal scale were calculated with the use of a Mantel–Haenszel test (trend test). The Kaplan–Meier method was used to estimate the cumulative incidence of NTM-PD and overall survival (OS) after the lung cancer surgery.

A multivariable Cox proportional hazard analysis with a backward stepwise selection with *p* < 0.05 for entry and *p* > 0.10 for removal was used to identify the independent risk factors related to NTM-PD development. The clinical stage of the tumor was not included in the multivariable analysis because it had significant collinearity with neoadjuvant and adjuvant treatments. All analyses were performed for both patients with NTM-PD and those who were NTM-positive, respectively. All tests were two-sided, and a *p*-value < 0.05 was considered significant. All statistical analyses were performed using SPSS software (IBM SPSS Statistics ver. 27, Chicago, IL, USA).
