Cancer of unknown primary in adolescents and young adults: Clinicopathological features, prognostic factors and survival outcomes

Background: Cancer in adolescents and young adults (AYAs) (15-39 years) is increasingly recognized as a distinct clinical and biological entity. Cancer of unknown primary (CUP), a disease traditionally presenting in older adults with a median age of 65 years, poses several challenges when diagnosed in AYA patients. This study describes clinicopathological features, outcomes and challenges in caring for AYA-CUP patients. Methods: A retrospective review of 47 AYAs diagnosed with CUP at MD Anderson Cancer Center (6/2006-6/2013) was performed. Patients with favorable CUP subsets treated as per site-specific recommendations were excluded. Demographics, imaging, pathology and treatment data was collected using a prospectively maintained CUP database. Kaplan-Meier product limit method and log-rank test were used to estimate and compare overall survival. The cox-proportional model was used for multivariate analyses. Results: Median age was 35 years (range 19-39). All patients underwent comprehensive workup. Adenocarcinoma was the predominant histology (70%). A median of 9 immunostains (range 2-29) were performed. The most common putative primary was biliary tract based on clinicopathological parameters as well as gene profiling. Patients presented with a median of 2 metastatic sites [lymph node (60%), lung (47%), liver (38%) and bone (34%)]. Most commonly used systemic chemotherapies included gemcitabine, fluorouracil, taxanes and platinum agents. Median overall survival for the entire cohort was 10.0 (95% confidence interval (CI): 6.7-15.4) months. On multivariate analyses, elevated lactate dehydrogenase (Hazard ratio (HR) 3.66; 95%CI 1.52-8.82; P = 0.004), ≥3 metastatic sites (HR 5.34; 95% CI 1.19-23.9; P = 0.029), and tissue of origin not tested (HR 3.4; 95%CI 1.44-8.06; P = 0.005) were associated with poor overall survival. Culine's CUP prognostic model (lactate dehydrogenase, performance status, liver metastases) was validated in this cohort (median overall survival: good-risk 25.2 months vs. poor-risk 6.1 months). Conclusions: AYA-CUP is associated with a poor prognosis. In the current "-omics" era collaborative research efforts towards understanding tumor biology and therapeutic targets in AYA-CUP is an unmet need, necessary for improving outcomes in young CUP patients.