Prognosis of sub-types of cancer of unknown primary (CUP) compared to metastatic cancer

Abstract

21010 Background: The aim is to study the clinical characteristics and outcomes of a complete cohort of presentations of Cancer of Unknown Primary (CUP) compared with patients presenting with metastatic cancer of known primary site. Methods: All persons diagnosed with cancer in New South Wales, Australia, from 1980 to 2004 were studied using a population based cancer registry. Patients classified as CUP were documented, compared to those with initial metastatic presentations of a known primary, for the same period. Results: There were 65,239 histologically or cytologically confirmed metastatic cancers presented. Of these 46,435 (77%) were metastatic with a known primary site and 13,280 (22%) were CUP. The median survival (ms) of all patients presenting with CUP was 3 months compared with 7 months for metastatic cancers of known primary site (p<0.0001). Patients with CUP with adenocarcinoma had significantly worse prognosis compared to metastatic adenocarcinoma of known primary site. However patients with squamous cell CUP had a significantly better outcome (ms 12 months) than metastatic squamous histology with a known primary site (ms 5 months, p<0.0001) with 31% of squamous cell CUP alive at 6 years. For those with CUP and adenocarcinoma the risk of dying was 80% greater compared to those with a known primary and adenocarcinoma (HR 1.8 95%CI 1.7–1.8). For those with CUP and squamous cell carcinoma the risk of dying was 50 % less (HR 0.49 95%CI 0.46–0.53). CUP with small cell, (HR 0.77 95%CI 0.71–0.85) and undifferentiated histology (HR 0.84, 95%CI 0.76–0.93) after controlling for sex and age, had a significantly better prognosis than other metastatic cancers. Germ cell CUP represented only 0.2% of all CUP presentations. Conclusions: CUP is a heterogeneous classification of cancer with a poorer prognosis overall when compared to metastatic cancer of known primary site especially if adenocarcinoma. However, squamous cell and small cell CUP had a better prognosis suggesting a need for specific and more focused treatment. Lack of trends for less CUP presentations compared to reducing metastatic cancer over this 24 year period suggests that CUP is in part a distinct clinico-pathological entity rather than a missed primary diagnosis. No significant financial relationships to disclose.