The Clinical Significance of Occult Gastrointestinal Primary Tumours in Metastatic Cancer: A Population Retrospective Cohort Study.
OBJECTIVE
The purpose of this study was to estimate the incidence of occult gastrointestinal (GI) primary tumours in patients with metastatic cancer of uncertain primary origin and evaluate their influence on treatments and overall survival (OS).


METHODS
We used population heath data from Manitoba, Canada to identify all patients initially diagnosed with metastatic cancer between 2002 and 2011. We defined patients to have "occult" primary tumour if the primary was found at least 6 months after initial diagnosis. Otherwise, we considered primary tumours as "obvious." We used propensity-score methods to match each patient with occult GI tumour to four patients with obvious GI tumour on all known clinicopathologic features. We compared treatments and 2-year survival data between the two patient groups and assessed treatment effect on OS using Cox regression adjustment.


RESULTS
Eighty-three patients had occult GI primary tumours, accounting for 17.6% of men and 14% of women with metastatic cancer of uncertain primary. A 1:4 matching created a matched group of 332 patients with obvious GI primary tumour. Occult cases compared to the matched group were less likely to receive surgical interventions and targeted biological therapy, and more likely to receive cytotoxic empiric chemotherapeutic agents. Having an occult GI tumour was associated with reduced OS and appeared to be a nonsignificant independent predictor of OS when adjusting for treatment differences.


CONCLUSIONS
GI tumours are the most common occult primary tumours in men and the second most common in women. Patients with occult GI primary tumours are potentially being undertreated with available GI site-specific and targeted therapies.
Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.|Ivey Business School, Western University, London, ON, Canada.
Malek B
MB
Hannouf
Department of Oncology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
Eric
E
Winquist
Department of Community Health Sciences, College of Medicine, Faculty of Health Sciences, University of Manitoba, Winnipeg, MB, Canada.
Salaheddin M
SM
Mahmud
Department of Oncology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.|Department of Surgery, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
Muriel
M
Brackstone
Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
Sisira
S
Sarma
Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.|Department of Radiation Oncology, London Regional Cancer Program, London, ON, Canada.
George
G
Rodrigues
Department of Biochemistry, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.
Peter K
PK
Rogan
Institute of Health Policy Management and Evaluation, University of Toronto, Toronto, ON, Canada.|Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto, ON, Canada.|Department of Public Health Sciences, University of California, Davis, CA, USA.
Jeffrey S
JS
Hoch
Department of Epidemiology and Biostatistics, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada.|Ivey Business School, Western University, London, ON, Canada.
Gregory S
GS
Zaric
D015331:Cohort Studies; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000453:epidemiology* / Q000401:mortality / Q000473:pathology*; D006801:Humans; D015994:Incidence; D008297:Male; D008350:Manitoba / Q000453:epidemiology; D008875:Middle Aged; D009362:Neoplasm Metastasis; D012189:Retrospective Studies; D016019:Survival Analysis
Cohort studies; Gastrointestinal neoplasms; Information storage and retrieval; Neoplasm metastasis; Propensity score; Research design; Unknown primary neoplasms