Abstract

Background

Patients with malignancy of undefined primary origin (MUO) present with metastatic disease on clinical examination or radiological imaging, without an obvious primary site. Following comprehensive investigation, including tissue biopsy, a primary site may be identified or a diagnosis of cancer of unknown primary (CUP) reached. The remaining patients, in whom comprehensive investigation is not possible, or medically sensible, retain the diagnosis of ‘MUO’. We sought to interrogate a large cancer centre database to define this MUO group and identify prognostic biomarkers to aid clinical decision making.

Method

A prospective data collection was undertaken of patients referred to the CUP service at the Edinburgh Cancer Centre between 2010-2019. Survival, defined as time from date of radiological diagnosis until death, or censorship if alive, was calculated. The modified Glasgow Prognostic Score (mGPS), a simple 3-point score (0-2) using albumin and CRP, at the time of clinical diagnosis was recorded.

Results

Data were available for 232 patients with MUO . Patient frailty (78%) was a frequent reason for not pursuing comprehensive investigation. Median survival in this group was 0.9 months. Biopsy was technically not possible in 10% of patients, in whom median survival was 3.7 months. 78% of patients with MUO had an elevated CRP (>10mg/l). mGPS stratified median survival from 2.3 months with mGPS 0 to 0.9 months with mGPS 2 (p=0.003).

Conclusion

Outcomes for patients with MUO are poor. Decisions not to pursue comprehensive investigations are based largely on subjective clinical assessment including performance status and suitability for anti-cancer therapy but can sometimes be difficult for patients, families and colleagues to understand. The mGPS, a bedside biomarker of the systemic inflammatory response, provides additional objective prognostic information in patients with MUO to aid shared decision making.