Primary mucinous carcinomas of the lung: Clinical characteristics and treatment outcomes.

INTRODUCTION: Invasive mucinous adenocarcinoma (IMA) of the lung is a distinct histologic variant of adenocarcinomas comprising about 2%-10% of lung adenocarcinomas. A large proportion of IMAs carry KRAS mutations and only rarely epidermal growth factor receptor (EGFR) mutations or ALK/ROS translocations; thus, most cases are not amenable for targeted therapy at present. This study was conducted to elicit the unique clinicopathological characteristics of IMA. MATERIALS AND METHODS: Medical records of patients diagnosed with IMA by needle biopsy at Kidwai Cancer Institute, Bangalore, from 2013 to 2018, were retrieved and reviewed. Statistical analysis was performed using SPSS version 23.0 (IBM Corp., Armonk, NY, USA). RESULTS: Four hundred and ninety cases of needle biopsy of the lung were diagonosed at our institute between January 2013 and December 2018. Nine cases (1.8%) were diagnosed as IMA. The median age of presentation was 59 years. Six (66.7%) were current smokers with pack-year > 20. Three (33.3%) of the cases were initially misdiagnosed as pneumonia in view of computed tomography findings. The lung was the most common site of metastasis (77.8%). Serum Carcinoembryonic Antigen (CEA) was elevated in six cases (66.7%). None of the cases had any driver mutations in EGFR gene or ALK and ROS1 translocations. All cases were treated with pemetrexed-carboplatin doublet followed by pemetrexed maintenance till progression. The median progression-free survival (PFS) was 15 months (range: 5-18 months). Docetaxel was given as the second-line chemotherapy in all progressed patients. Best response noted was stable disease, seen in 4 (57.1%) cases. The median PFS for docetaxel was 6 months (range: 3-8 months). The median overall survival was 22 months (range: 9-27 months). Patients with initially raised CEA at progression had a serial rise in serum CEA. CONCLUSIONS: IMA is rarely diagnosed on needle biopsies due to insufficient tissue. They mimic pneumonia on imaging, thus delaying diagnosis. EGFR mutations, ALK, and ROS1 translocations are usually negative making them ineligible for tyrosine kinase inhibitors. Response to chemotherapy is modest.