Epidemiology

Cancer of unknown primary may be limited to a set of cancers

Last Updated: 2011-01-13 10:30:20 -0400 (Reuters Health)

By Rob Goodier

NEW YORK (Reuters Health) - The elusive original tumors that cause diagnoses of metastatic cancers of unknown primary origin (CUP) may not be as random as previously thought.

A new Swedish study examining familial patterns has found that CUP may be limited to a set that includes kidney, lung and colorectal cancers.

"Familial clusters of CUP provide some etiological clues for the unknown primary, which is helpful for clinical genetic counseling," the lead researcher Dr. Xiaochen Shu, at Malm� University Hospital, Sweden, told Reuters Health in an email.

Dr. Xiaochen's team examined the records of 35,168 CUP patients in the Swedish Family-Cancer Database.

The researchers looked for concordant CUP, in which unidentified cancers struck two or more family members, and for discordant CUP, in which family members of CUP patients were diagnosed with identified cancer. The rationale, they write, was that the two associations allowed for independent analyses and a greater likelihood of significance.

For concordant associations, 2.8% of all CUP cases among the offspring generation were linked to CUP diagnoses among their parents' generation. And when a sibling was diagnosed with CUP, the standardized incidence ratio for CUP was 1.69.

That would put CUP associations among families on par with familial nervous system cancer, non-Hodgkin's lymphoma, or liver cancer.

For discordant associations between siblings, CUP was linked to cancers of the lung (with a standardized incidence ratio of 1.87), kidney (1.82), liver (1.67), ovarian (1.45), colorectal (1.26), and breast (1.15).

The researchers published the results December 28, 2010, online before print in the Journal of Clinical Oncology.

Dr. Xiaochen's team points out that they observed four independent associations in families between CUP and lung cancer, three associations between CUP and colorectal cancer, and two between CUP and each of liver, ovarian and kidney cancers.

CUP is diagnosed in 2-4% of cancer patients, according to the National Cancer Institute and the number has dropped sharply in the last decade, probably thanks to improved cancer diagnostic techniques.

"Mechanistic exploration of CUP may provide insight into defense against primary tumors and the metastatic process," Dr. Xiaochen's team writes. Dr. Xiaochen added that he may investigate the role of environmental factors in CUP in future studies.

Source: http://bit.ly/gg0pFg

J Clin Oncol 2010.