Background Pulmonary adenocarcinoma has become the most common histological subtype of non-small cell lung cancer. It originates in the glandular cells of lung tissue. It is characterized by slow growth and a tendency to metastasize. Early detection is crucial for prognosis and effective treatment. In its early stages, it typically appears on tomography as ground-glass nodular lesions; however, it can manifest in various ways, posing a diagnostic challenge.

Case Presentation A 76-year-old female Jehovah's Witness, accountant, with controlled type II diabetes, arterial hypertension, and a hysterectomy for myomatosis at age 45. She began experiencing a dry cough in August 2021, which progressed over a year to the point of causing dyspnea, accompanied by a weight loss of 10 kilograms, denying any fever or night sweats. She was referred to a tertiary hospital where an initial diagnosis of multinodular disease was made (Fig. 1 and 2), and a bronchoscopy was performed, revealing only a positive result for galactomannan in bronchoalveolar lavage. Treatment with itraconazole was started without improvement. Due to persistent symptoms, a new bronchoscopy was performed in August 2022, which documented adenocarcinoma cells in bronchial fluid cytology but not in biopsy, leading to another biopsy via Video Assisted Thoracoscopic Surgery, with the following results:

Histopathological Report: Pulmonary adenocarcinoma with a lipidic, mucinous pattern,immunohistochemistry: TTF1 negative, CK7 and CK20 positive, enteric variety. Negative mutation panel. PDL1 0%.

Given the clinical stage IV due to multinodular pulmonary disease without mutations, chemotherapy with carboplatin/pemetrexed was decided upon. After the third cycle of chemotherapy, a new chest CT scan showed an unusual response pattern with multiple cystic lesions where the previous lesions had been (November 2022). Due to clinical stability, the same chemotherapy regimen was maintained, with a follow-up CT scan planned for February2023.

Discussion The unusual change from nodules to cystic lesions in pulmonary adenocarcinoma represents a rare diagnostic challenge. This case provides valuable insight into the atypical variants of the disease and their clinical implications, addressing from the initial clinical presentation to diagnostic confirmation