Glioblastoma recurrence followed by newly diagnosed small cell lung cancer: a case report on personalized concurrent chemoradiotherapy and therapeutic considerations.

Glioblastoma (GBM) and small cell lung cancer (SCLC) are both highly aggressive malignancies, and their co-occurrence is extremely rare, posing significant therapeutic challenges. We report a 50-year-old male diagnosed with right temporal GBM (WHO grade IV) in 2014, who underwent surgery and the standard Stupp regimen (radiotherapy with temozolomide, TMZ), achieving a progression-free survival (PFS1) of 42 months. During re-irradiation with TMZ for the first GBM recurrence, a second primary tumor-SCLC (cT3N2M0, Stage IIIB)-was identified 45 months after the initial diagnosis. For this rare dual malignancy, an individualized concurrent chemoradiotherapy approach was implemented: continued cranial radiotherapy with TMZ alongside etoposide plus platinum (EP) chemotherapy and subsequent palliative thoracic radiotherapy for the lung tumor. Treatment was well-tolerated with no grade ≥3 adverse events, resulting in partial response of the pulmonary lesion and stable intracranial disease for 10 months. The patient experienced a PFS2 of 10 months after the second GBM recurrence and a PFS of 13 months for SCLC, with an overall survival (OS) of 58 months from initial GBM diagnosis-substantially exceeding the typical prognosis for either tumor alone. This case suggests that an individualized concurrent chemoradiotherapy strategy may achieve dual tumor control and confer meaningful survival benefits in patients with recurrent GBM and metachronous SCLC.