A Case of Advanced Anaplastic Lymphoma Kinase-positive Lung Adenocarcinoma During the Third Trimester of Pregnancy

━━ Background. Lung cancer is a rare complication of pregnancy. Lung cancer may be diagnosed at an advanced stage because respiratory symptoms can be mistakenly perceived as pregnancy-related, and radio-logical examinations will probably be avoided due to concerns regarding fetal exposure. Case. A pregnant woman in her late thirties complained of cough that started from approximately the 26 th week of gestation, gradually re-sulting in dyspnea and appetite loss. Because a chest X-ray performed during the 37 th week of gestation revealed opacity in the entire left lung field, she was immediately admitted to our hospital. Computed tomography revealed total atelectasis of the left lung accompanied by pleural effusion, bilateral hilar and mediastinal lymphadenopathies, and multiple nodular shadows in the right lung. Considering the possibility of carcinomatous pleuritis due to lung cancer, continuous suction drainage of the left pleural effusion was immediately initiated. The follow-ing day, her infant was delivered via cesarean section. Pathological and genetic examinations of the pleural effusion sample demonstrated adenocarcinoma and rearrangement of the anaplastic lymphoma kinase (ALK) gene. After initiating alectinib treatment on the 5 th day of hospitalization, the tumor promptly decreased in size and the therapeutic effect has been maintained for more than 1 year. No malignant tumors or developmental anomalies have been observed in her infant. Conclusion. Lung cancer in women of reproductive age is characterized by a relatively high frequency of harboring certain driver gene mutations, which can progress rapidly. Thus, chest X-ray imaging should be performed for patients with persistent respiratory symptoms. Additionally, considering the possibility of the transmission of maternal cancer to offspring, pathological examinations of the motherʼs pla-centa and postnatal follow-up of the infant are important. ( JJLC. 2022;62:1009-1013)