L-LCNEC is a rare subtype of lung cancer classification. According to the existing literature reports, the average age of L-LCNEC was 60 years old, most of those were male [14], which was similar to our results. The survival rate of L-LCNEC greatly varied due to the selected patients’ age, tumor stage or treatment difference[15–23]. Clinicians' prediction for the survival probability of L-LCNEC is often based on the large-population study, but the estimation of an individual survival rate is puzzling. Therefore, it is necessary to establish a more accurate model to predict the prognosis of L-LCNEC and provide more effective treatment measures for individuals. Based on a retrospective study of high-quality, population-based data, our study summarized the clinical characteristics of patients with L-LCNEC, analyzed the factors related to the prognosis and established a more reasonable and effective nomogram model for predicting survival rate of L-LCNEC.
Our results indicated that the independent factors influencing the prognosis of L-LCNEC were age at diagnosis, sex, stage of tumor, surgical treatment, radiotherapy and chemotherapy.
Compared with patients under 60 years old, there was an increased risk of death in patients over 60 years old. Increased risk in elderly groups may be due to their poor physical function, intolerance or insensitivity to surgery, chemotherapy, radiotherapy or other treatment methods, as well as multiple diseases combination. In terms of gender, the prognosis of male patients was worse than female patients, which may be related to the factors such as more smoking phenomenon involved in male patients or their different body functions or characteristics from female. Similar to other tumors, TNM staging is an independent factor for the prognosis of L-LCNEC patients. Compared with stage I patients, the risk of death in stage II patients increased by 1.06 times, stage III patients increased by 1.35 times, and stage IV patients increased by 3.02 times, thus suggesting that with the tumor staging increase, the risk of death in patients also increased. The possible reason is that the patients' body function is worse and the more complications appear with the advanced tumor stage, they are unable to receive comprehensive treatment for tumors.
There is no standard treatment method for L-LCNEC. Similar to other subtypes of lung cancer, combined therapy, including surgery, chemotherapy and radiotherapy, were taken. The beneficial effect of surgery on L-LCNEC patients has been reported in the previous literatures[24, 25]. Surgical-predominant therapy should be the principle method for treating L-LCNEC patients with early stage presently. Our study indicated surgery was an independent factor affecting the prognosis of L-LCNEC. However, the effect of surgery on the prognosis of L-LCNEC patients was also related to the surgical method. Compared with the patients who did not undergo surgery treatment, the results showed that the mortality risk of patients received local tumor destruction was reduced by 29.4%, but there was no statistical significance (P = 0.729), while the mortality risk of those received sublobar resection, lobectomy and pneumonectomy was reduced by 47.1% (P = 0.000), 61.3% (P = 0.000), 61.2%(P = 0.000)respectively. Therefore, surgical treatment may not be limited to stage I L-LCNEC patients, but should be extended to resectable patients after adjuvant chemotherapy. Lobectomy or pneumonectomy could be conducted as soon as possible if the patient's physical condition allowed, because the cancer cells grow rapidly and patients may lose the chance of surgery within a few months.
L-LCNEC is aggressive with high potential to metastasize and is easy to recur after operation, so it is not enough to effectively treat the disease by surgery alone. L-LCNEC patients treated by surgery alone were rarely cured even in the early stage [26], which urges more scholars to consider chemotherapy or radiotherapy [6, 18, 27, 28]. Two retrospective analysis showed that compared with the patients with surgery alone, platinum-based neoadjuvant chemotherapy or postoperative adjuvant chemotherapy could prolong the recurrence time of tumor and significantly benefit the long-term survival for the patients with early stage [29, 30]. Chemotherapy regimens for small cell lung cancer/non-small cell lung cancer were used in L-LCNEC treatment, but most of the data were came from single center, small sample or retrospective studies, and the results were controversial [7, 31, 32]. For patients with advanced L-LCNEC, chemotherapy could significantly improve overall survival [33–36]. Our study also showed that chemotherapy may have a survival advantage. Since SEER database does not contain records of chemotherapy regimens, the topic which chemotherapy is better for L-LCNEC patients was not involved in our study.
Because of the low incidence, there were a few literatures on radiotherapy for L-LCNEC. Mackley believed that if gross residual disease was present after surgery, adjuvant radiation should be recommended, adjuvant radiotherapy could be beneficial to local control and reduced the risk of local recurrence [37]. Rieber conclued that patients with incomplete resection showed a survival benefit from adjuvant radiotherapy [38]. Our results also supported the prognostic benefits of radiotherapy.
Through the establishment of nomogram, we could predict individualized prognosis according to their scores in order to select an appropriate treatment strategy for individuals.
There were some limitations in our study: this was a retrospective study, our results are inevitable subject to selection bias. In addition, due to the limited clinical factors included in SEER database, this study did not analyze the possible factors related to the prognosis of the disease, such as smoking record, genes status, chemotherapy schemes, ect.. Therefore, it is necessary for a prospective evaluation for the nomogram in clinical application.