Lung parenchymal invasion in pulmonary carcinoid tumor: an important histologic feature suggesting the diagnosis of atypical carcinoid and poor prognosis

Treatment of Pulmonary Carcinoid Tumors With Bronchoscopic Cryotherapy: A 28-Year Single-center Experience

BACKGROUND

Pulmonary carcinoids are rare tumors originating from neuroendocrine cells in the lungs. Because of their potentially infiltrative nature, surgical resection remains the treatment of choice. However, not all patients with technically resectable disease will be able to undergo surgery, primarily because of poor lung function or medical co-morbidities. Centrally located, intraluminal tumors have been reported to be amenable to bronchoscopic treatment. We specifically examined the role of cryotherapy in the treatment of bronchial carcinoid tumors.

METHODS

Sixty-three patients (52.38% female) who underwent a combined total of 243 cryotherapy procedures for treatment of bronchial carcinoid between 1992 and 2020 in our institution were included in the study. Following discussion in multidisciplinary meetings, patients were considered for first-line cryotherapy when lung resection was deemed not possible or when they had rejected surgery.

RESULTS

Cryotherapy resulted in complete remission in 21 (33.33%) patients with maximum tumor diameter less than 20 mm (mean: 11.08 mm, 95% confidence interval: 8.76-13.40), and allowed 22 (34.92%) patients with larger lesions (mean: 24.04 mm, 95% confidence interval: 18.78-29.30) to proceed with parenchymal sparing resections. Marked symptomatic relief (P<0.001) was reported by 58 (92.06%) patients. The median follow-up was 33 months (range: 0 to 243 mo). One (1.59%) patient was diagnosed with recurrence in a contralateral lobe 3 years after surgery and was treated with radiofrequency ablation.

CONCLUSIONS

In the absence of a definitive randomized controlled trial comparing bronchoscopic treatment with surgical resection, we provide evidence on the safety and efficacy of cryotherapy and encourage wider adoption of this inexpensive and minimally invasive technique for treatment of bronchial carcinoids.

[Systemic Therapy for Low-grade Pulmonary Neuroendocrine Tumor]

肺部是神经内分泌肿瘤（neuroendocrine tumor, NET）的第二好发部位。肺类癌包括典型类癌和不典型类癌，属于低级别神经内分泌肿瘤。这一类肿瘤由于发病率较低，目前尚未得到广大医务工作者的重视。但有效的治疗不仅能提高患者的远期生存，还能控制患者症状，改善生活质量。本文分别阐述肺低级别神经内分泌肿瘤的流行病学和病理学特点、早期患者的治疗策略以及进展期患者的治疗策略。早期患者应当尽早进行手术治疗。进展期患者治疗方式包括化疗、SSAs、mTOR抑制剂、肽受体介导的放射性核素治疗、生物治疗以及靶向治疗。目前的研究结论大多来自其他部位的NETs研究外推而来，仍需针对肺低级别神经内分泌肿瘤患者进行特异性临床试验加以证实。

Lung neuroendocrine tumors: pathological characteristics

Lung neuroendocrine tumors (NETs) are a heterogeneous family of neoplasms comprising four histologic types, namely typical and atypical carcinoid (TC and AC), large-cell neuroendocrine and small cell carcinoma (SCC). Classification criteria include the number of mitoses per 2 mm2, the occurrence and extent of necrosis, cytological and histological features and immunohistochemistry for neuroendocrine markers. The classification system and the diagnostic workflow of lung NETs are apparently easy to apply and well established. However, several unresolved issues still exist in classification and pathological characterization of these tumors, probably because inter-observer diagnostic reproducibility remains disappointing, likely due to inconsistency in recognizing necrosis, mitoses and cytological details, especially in small biopsy or cytological materials. Furthermore, the lack of strong prognostic and grading criteria leads to the incomplete interpretation of some rare intermediate entities that stand in between AC and large cell neuroendocrine carcinoma (LCNEC) categories.

Classification of lung neuroendocrine tumors: lights and shadows

Neuroendocrine tumors of the lung are classified into low-grade typical and intermediate-grade atypical carcinoids, and high-grade poorly differentiated neuroendocrine carcinomas of the large and small cell types. This scheme is strongly predictive of patients' prognosis but relies on few and scarcely reproducible pathological parameters (namely mitotic count and assessment of the presence of necrosis), which have been demonstrated to affect the inter-observer agreement of the classification. Moreover, tumor and nodal staging schemes are not specific for lung carcinoids, at variance with neuroendocrine tumors of the gastro-entero-pancreatic system, despite these tumors have specific features that strongly differ from conventional lung cancer. Finally, there is no grading for lung neuroendocrine neoplasms and prognostication, as well as the definition of treatment modalities and clinical strategies, which are based on tumor histotypes, only. However, literature data indicate that the evaluation of Ki-67 proliferation index may be a reliable and useful tool to determine the biological and clinical behavior of neuroendocrine tumors, with special reference to carcinoids, both in pre-operative and surgical samples.