Discussion
General treatment patterns
Patterns of care indicate that most early stage NSCLC cases receive surgery and/or radiotherapy. However, whereas the percentage receiving radiotherapy increased with advancing stage, the percentage receiving surgery decreased with advancing stage. This likely reflects the increasing difficulty of performing more extensive surgical resections, even among those with stage IA–IIB disease.
Uptake of MIS and rate of conversions
The use of MIS among surgically treated cases increased over time, up to 48.6% among stage IA cases in 2014. This increasing uptake of MIS was robust across the different conducted sensitivity analyses. Our findings are similar to those in a recent study, in which 44.5% of wedge resections and lobectomies among patients with non-metastatic lung cancer in Veterans Affairs hospitals between 2012 and 2015 were conducted using VATS.14 The European Thoracic Surgery Database, which collects data from 170 hospitals across 22 European countries, reported that the uptake of VATS lobectomies increased from 5.4% in 2007–2011 to 29.3% in 2012–2015.20 Thus, it appears that the uptake of MIS in Europe is also increasing, although its uptake may lag compared with the USA.20 In the UK, the uptake of MIS is similar to the USA; increasing from 53.4% in 2016 to 55.8% in 2017.21 Rates of conversions were similar in the UK (10.6% of lobectomy and bilobectomy procedures in 2017), compared with our US-based study (11.5% of lobectomy and bilobectomy procedures in 2014).21 The increasing use of MIS may particularly benefit patients with a reduced lung function or cardiopulmonary reserve, in whom this approach has been shown to reduce rates of pulmonary morbidity compared with open surgery.22
While we confirm that the uptake of MIS is increasing, we add that the rate of conversions to open surgery decreased during the same period. This may reflect increasing experience of thoracic surgeons.23 Whereas the uptake of MIS decreased with advancing stage, the rate of conversions increased with advancing stage. This finding may be partly explained by the decreasing use of sublobar resections and the increasing use of pneumonectomy with advancing stage. Indeed, the uptake of MIS was lower for more extensive resections (eg, pneumonectomy < (bi)lobectomy < sublobar resection). These observations may reflect the technical difficulty of performing more extensive resections by MIS.
In the USA, annual lung cancer screening has been recommended for high-risk individuals.7 It has been estimated that the full-scale implementation of lung cancer screening in the USA will shift the percentage of stage I diagnoses in the general population (which includes individuals that are not eligible for screening) from 22.2% to 30.6%.6 This will increase demand for lung cancer surgery in the USA by up to 37.0%.6 If screening is to be effective, these cases should receive optimal treatment by MIS resection in a high-volume hospital.24 25 Therefore, we expect that the uptake of MIS in the USA will continue to increase in coming years. In Europe, lung cancer screening has not yet been implemented. Nevertheless, several European countries have expressed the intention to start planning for the implementation of lung cancer screening.8 Therefore, we expect that the uptake of MIS lung resections will continue to increase in Europe as well.
Uptake of SBRT
Among patients with stage IA–IB NSCLC, the uptake of SBRT increased substantially between 2010 and 2014. This finding was robust to the different sensitivity analyses. The increasing uptake of SBRT may particularly benefit patients with lung cancer with comorbidities, which can increase the risks related to surgery. In the Netherlands, Palma and colleagues demonstrated that an increased use of SBRT among patients with stage I NSCLC led to fewer untreated elderly patients.26 In our US-based study, the overall percentage of early stage patients that received radiotherapy (both SBRT and conventional radiotherapy) also increased (by 3.4 percentage points). However, we did not find a corresponding reduction in the rate of non-treatment. Instead, we found that the percentage of early stage cases that received surgery decreased by 3.5 percentage points. This suggests a possible shift from operable patients towards medically inoperable patients (eg, due to comorbidities), which should be further investigated in future studies. The constant non-treatment rate of approximately 10% suggests possibilities for a further increase in the use of radiotherapy, and in particular SBRT, among early stage cases that would otherwise not receive any treatment.
Currently, SBRT is only recommended for medically inoperable early stage NSCLC cases. However, some studies have suggested that SBRT may be feasible in medically operable patients,27 which could increase the future uptake of SBRT. Because lung cancer screening is only recommended for patients fit to undergo curative lung surgery,7 it’s continued implementation may not directly increase the future use of SBRT. However, in practice it may be difficult to assess fitness for surgery prior to screening. Therefore, the increase in early stage cases due to screening may still lead to a further increase in the use of SBRT. Consequently, it is likely that the uptake of SBRT will continue to increase.
The uptake of SBRT was modest but present among stages IIA and IIB. This is most likely due to concerns about either lymph node involvement, tumour size or size of the irradiated field. SBRT is indeed most appropriate for tumours smaller than 5 cm (which encompasses stage I–IIA). Nevertheless, SBRT may also be used for larger isolated tumours (T1–3, N0, M0).5 28
Strengths and limitations
The most important strength of this current analysis is the use of the NCDB data set, which captures treatment data on 70% of incident cancer cases in the USA. Although this database is facility-based, an earlier report found no major differences in the distributions of sex, age, race or ethnicity, health insurance status, histology, and stage between lung cancer cases in the NCDB and the population-based Surveillance, Epidemiology, and End Results data set.17 Therefore, in contrast to previous reports, the findings of our study are likely representative for the general US population.14
A possible limitation of our study is the lack of clinical information in the NCDB, such as performance status. Therefore, we could not determine whether cases were medically operable or not. Future research is necessary to determine whether cases that do not receive any treatment may have been medically eligible for surgery or SBRT.
A second possible limitation of using cancer registry data is that coding practices may change over time. However, the AJCC seventh edition staging manual was almost exclusively used during the study time period, which limits changes in study eligibility over time. In addition, no changes occurred in the coding of any of the outcome variables (eg, surgical approach, surgical extent or radiation modality).
A third limitation is that we did not assess whether the increasing use of MIS and SBRT affected patient outcomes. The NCDB does not include patient-reported outcomes, such as quality of life. In addition, we feel that a prospective randomised trial is the best method to provide an unbiased comparison of oncological outcomes across treatment modalities. Recently, the prospective VIdeo-assisted thoracoscopic lobectomy vs conventional Open LobEcTomy for lung cancer Trial confirmed that that VATS lobectomy is associated with significantly lower in-hospital complications and a shorter length of stay than open lobectomy, without compromising oncological outcomes.29 Another recent prospective randomised controlled trial, which included inoperable stage I NSCLC cases, showed that SBRT provides superior tumour control compared with standard radiotherapy, without increasing toxicity.30 These studies indicate that the increasing uptake of MIS and SBRT in the USA will likely provide clinical benefit to patients with early stage NSCLC.