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Introduction Lymphangitic carcinomatosis (LC) is a pattern of metastasis where tumor spreads along the pulmonary parenchymal lymphatics which produces a characteristic pattern of interlobular septa and axial peribronchial thickening. This pattern of metastatic disease is most typically associated with advanced disease and is observed in a range of malignancies including breast, lung, colon, and genitourinary origin. The presence of LC is usually associated with a poor prognosis and is readily detectable by computed tomography (CT) . To date, there is limited data in the literature describing the occurrence of LC in MPM or its prognostic significance [2,3]. MPM typically progresses through local extension in the pleural space and through adjacent structures such as the chest wall and diaphragm. Metastasis from MPM to the regional lymph nodes is also very common; however, the extension of tumor into the pulmonary lymphatics currently is less well characterized. In a previous review of 200 patients with MPM, 13.5% displayed lymphangitic involvement of the lung parenchyma on pathology . However, apart from this study, LC in MPM has not been well described, with no literature, to our knowledge, describing LC as a pattern of local relapse in the post-pleurectomy/decortication population. Extended pleurectomy/decortication (EPD) is performed in MPM with the intent to achieve a gross macroscopic resection and entails stripping of the parietal and visceral pleura, leaving the uninvolved lung intact . By leaving the lung intact, EPD is generally associated with a lower post-operative morbidity and possibly better overall survival compared to en block extrapleural pneumonectomy (EPP), though this is an area of active research and discussion in the MPM Necrosulfonamide [, , , , , ]. Given the potential for increased risk of retained microscopic residual disease in EPD  compared to EPP, at our institution, most patients also receive intraoperative pleural photodynamic therapy (PDT) with the goal of eradicating residual microscopic disease . With all therapy for MPM, the failure rate is high and an improved understanding of the predictive and prognostic implications of radiologic findings is important for disease management and prognostication .
Discussion Pulmonary LC is a pattern of tumor metastasis that has been described for a range of primary malignancies , most commonly breast cancer, lung cancer and cancers of gastrointestinal origin. The incidence of LC has been estimated at approximately 6–8% in some cancers  and generally portends a worse prognosis. There is little published literature describing the incidence of LC in MPM. To the best of our knowledge, this is the first report characterizing the incidence of this pattern of metastasis in MPM patients who have undergone lung-sparing EPD. When LC occurred in our cohort, it presented in the ipsilateral lung, possibly a consequence of the disrupted pleural barrier to local extension of disease in the pleurectomy space into the lung. Bilateral disease occurred in 2 patients with diffuse LC. Here we have demonstrated that the LC pattern of metastasis is a common pattern of failure in the post-EPD setting with the radiographic appearance of LC in patients (39%) who undergo EPD with intraoperative PDT for MPM. This is in keeping with the reported incidence of 44% lymphatic invasion in a population of epithelioid diffuse MPM reported by Kadota et al . This suggests that the performance of EPD, at least when performed together with PDT, does not result in an increased incidence in LC compared to the non-surgical population. However since PDT is intended to destroy microscopic tumor after macroscopic resection (5), it is possible that the use of this intraoperative technique in our population may have decreased the rate of LC and increased OS and PFS in our cohort compared to patients that do not undergo PDT.