Complete remission following targeted therapy in BRAF V600E: mutant pulmonary lymphangitic carcinomatosis secondary to rectal cancer—a case report

BACKGROUND: Pulmonary lymphangitic carcinomatosis (PLC) secondary to colorectal cancer is an uncommon manifestation, accounting for fewer than 7% of all PLC cases. Because of its nonspecific clinical and radiologic features, it is frequently misdiagnosed as interstitial lung disease or pulmonary infection. The prognosis remains poor, as the majority of patient's progress rapidly to acute respiratory failure shortly after diagnosis, with a reported median survival ranging from 2.2 to 7 months. To date, only one documented case has demonstrated survival beyond 12 months. Here, we present a patient who survived 19 months, emphasizing the importance of early recognition and the role of molecular-guided therapy in extending survival. CASE PRESENTATION: We present a case of PLC secondary to rectal cancer harboring a BRAF V600E mutation that achieved complete response after relapse with triple combination therapy (dabrafenib, trametinib and cetuximab). A 30-year-old Vietnamese woman presented with unresectable rectal carcinoma and multiple lymph node metastases. She was initially treated with FOLFOX plus bevacizumab, achieving a first complete response, followed by FOLFIRI plus bevacizumab. However, she subsequently developed progressive pulmonary lymphangitic carcinomatosis with impending respiratory failure. Given the BRAF V600E mutation, third-line treatment with a BRAF inhibitor and trametinib combined with cetuximab was initiated. This regimen led to rapid symptomatic improvement, with dyspnea resolving within 1 day, and resulted in a second complete remission, specifically of pulmonary lymphangitic carcinomatosis, which was maintained for 4 months. Despite subsequent disease progression, the patient achieved an overall survival of 19 months from the time of diagnosis. CONCLUSIONS: This case demonstrates that triple combination therapy may induce rapid and durable remission in PLC secondary to BRAF-mutated colorectal cancer. It underscores the importance of comprehensive molecular profiling in guiding personalized treatment for rare metastatic manifestations. Moreover, this report highlights the importance of timely, genomics-guided therapeutic decision-making and pragmatic adaptation of targeted strategies in managing aggressive BRAF V600E-mutant colorectal cancer, particularly in clinically complex and resource-constrained settings.