Pulmonary Low Malignant Potential Adenocarcinoma: A Validation of the Proposed Criteria for This Novel Subtype

Adenocarcinoma (ADC) is the most common histologic type of lung cancer, including in situ (lepidic), minimally invasive, and invasive forms. While the former 2 types are associated with a favorable outcome, the latter includes tumors with variable behavior, often tumor stage-related. A recent study proposed strict morphologic criteria defining a new subgroup of resected stage I invasive ADC (16% of cases) with favorable outcomes (100% disease-specific survival), named "ADC of low malignant potential (LMP-ADC)." The following criteria were met: ≤3 cm size, nonmucinous histotype, ≥15% lepidic growth, and the absence of the following: high-grade patterns, >1 mitosis/2 mm 2 , necrosis, and vascular/pleural invasion. The aim of the present study was to validate the performance of such criteria to identify LMP-ADC in a series of 274 stage IA resected lung ADCs from a single institution. Thirty-four tumors (12.4%) met the proposed criteria for LMP-ADC, as confirmed by additional stains for mitotic figures, Ki67 index, and elastic fibers (helpful to assess alveolar wall invasion). Minor differences between the lepidic and invasive components were observed regarding cell atypia and proliferation. p53 was normally expressed by invasive tumor cells. Mutations occurred in known lung cancer genes (mostly KRAS and EGFR). Five patients (14.7%) developed disease progression and 2 of them (5.9%) died of the disease. In our series, the disease-specific survival was 94.1%. In conclusion, in resected invasive lung ADC, a subgroup presenting low-grade morphologic features and associated with favorable prognosis does exist. Morphologic criteria for LMP-ADC supported by ancillary techniques represent a valid tool to better define this novel subgroup and to refine the stratification of invasive lung ADC, possibly suggesting modified follow-up protocols, based on the observed indolent behavior in most cases.

Pulmonary Hamartoma Associated With Lung Cancer (PHALC Study): Results of a Multicenter Study

Purpose

Pulmonary hamartoma is the most common benign tumor of the lung. We analyzed a 20-year historical series of patients with pulmonary hamartoma undergoing surgical resection, aiming to evaluate the characteristics, the outcomes, and the association between hamartoma and lung cancer.

Methods

It was a retrospective multicenter study including the data of all consecutive patients with pulmonary hamartoma undergoing surgical resection. The end-points were to evaluate: (i) the characteristics of hamartoma, (ii) outcomes, and (iii) whether hamartoma was a predictive factor for lung cancer development

Results

Our study population included 540 patients. Upfront surgical or endoscopic resection was performed in 385 (71%) cases while in the remaining 155 (29%) cases, the lesions were resected 20 ± 3.5 months later due to increase in size. In most cases, lung sparing resection was carried out including enucleation (n = 259; 48%) and wedge resection (n = 230; 43%) while 5 (1%) patients underwent endoscopic resection. Only two patients (0, 2%) had major complications. One patient (0.23%) had recurrence after endoscopic resection, while no cases of malignant degeneration were seen (mean follow-up:103.3 ± 93 months). Seventy-six patients (14%) had associated lung cancer, synchronous in 9 (12%) and metachronous in 67 (88%). Only age > 70-year-old (p = 0.0059) and smokers > 20 cigarettes/day (p < 0.0001) were the significant risk factors for lung cancer.

Conclusion

PH was a benign tumor, with no evidence of recurrence and/or of malignant degeneration after resection. The association between hamartoma and lung cancer was a spurious phenomenon due to common risk factors.