Pathological and imaging features of pulmonary invasive mucinous adenocarcinoma-a retrospective cohort study.

Background: Pulmonary invasive mucinous adenocarcinoma (IMA) is a rare subtype of lung cancer which is easily misdiagnosed as inflammatory nodules, tuberculosis, pulmonary diffuse lesions, or hamartomas due to the lack of clinical specificity. This study aims to identify the pathological and imaging characteristics of IMA, which will favor to improve the diagnostic and therapeutic efficacy.

Methods: A retrospective study was conducted by enrolling patients histopathologically diagnosed with pulmonary IMA in the current study between January 2014 and December 2021. The clinical pathological and radiological data were collected for analysis to evaluate the radiological patterns and pathological and molecular characteristics of IMA.

Results: A total of 136 patients were included in the study, of whom 58 were male and 78 were female. The patients had an average age of 63.0±9.7 years. The tumors were classified into the following three pathological types: pure mucinous (76 cases) featured by only mucinous cells observed under the microscope; mixed mucinous (23 cases) featured as an attached-wall, papillary, acinar, and solid tumor cells with more than 10% mucinous cells.; and mucinous-absent (29 cases) featured with the absence of mucous cells, but still can detect more than 10% of mucin expresses. In terms of the morphological classification based on the CT scans, 88 (64.7%) cases were identified as the nodular type, 31 (22.8%) as the inflammatory type, 15 (11.1%) as the mass-like type, and two (1.5%) as the diffuse type. For the molecular features, patients afflicted with IMA showed much lower levels of thyroid transcription factor-1 (15%) than those with usual adenocarcinoma (over 80%). However, cytokeratin 20 was more common in IMA (50%) than the usual adenocarcinoma (about 5%). The K-RAS mutation was prevalent in 75% of IMA, which contrasted sharply to its occurrence in a mere 15% of the usual adenocarcinoma. Epidermal growth factor receptor mutations were rarer in IMA (less than 5%) than the usual adenocarcinoma (about 50%).

Conclusions: The pathological and imaging features enrich our understanding of the disease's heterogeneity, which will contribute to more personalized diagnostic and therapeutic strategies.