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Relatives of Patients With Carcinoma of Unknown Primary at Increased Risk for This and Other Cancers

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Key Points

  • Relatives of patients with carcinoma of unknown primary are at increased risk of developing it themselves as well as several other malignant neoplasms, including lung, pancreatic, and colon cancers; non-Hodgkin lymphoma; and myeloma.
  • Some of these associations were moderately strong, especially the 43% elevated risk of lung cancer.
  • Relatives should be encouraged to modify risk factors and be screened for colorectal cancer. 

Relatives of patients with carcinoma of unknown primary are at increased risk of developing it themselves as well as several other malignant neoplasms, including lung, pancreatic, and colon cancers; non-Hodgkin lymphoma; and myeloma, according to a study published in JAMA Oncology. “Some of these associations were moderately strong, especially the carcinoma of unknown primary–lung cancer association, with a 43% elevated risk of lung cancer” in first-degree relatives of patients with carcinoma of unknown primary, noted N. Jewel Samadder, MD, MSc, of the Huntsman Cancer Institute, University of Utah, Salt Lake City, and coauthors.

“Relatives of patients with carcinoma of unknown primary should be aware of the elevated risks for lung, pancreatic, and colon cancers and encouraged to modify risk factors and adhere to site-specific population cancer screening,” the investigators advised. “These findings should provide physicians with further evidence to encourage smoking avoidance or cessation and encourage colorectal cancer screening.”

Median Survival of 3 Months

The authors noted that carcinoma of unknown primary “accounts for 3% to 5% of all human cancer cases and is reported to be the seventh or eighth most frequent category of malignant neoplasm and the fourth most common cancer-related cause of death in both sexes.” The most common cases of carcinoma of unknown primary are adenocarcinomas, squamous cell carcinomas, and undifferentiated neoplasms. “The combination of advanced stage, aggressive behavior, and uncertain treatment approaches leads to poor prognosis,” the researchers stated. The reported median survival for patients with carcinoma of unknown primary in the United States is 3 months.

To quantify the risk of cancer by site in relatives of patients with carcinoma of unknown primary, the investigators conducted a nested case-control study of patients diagnosed with carcinoma of unknown primary between 1980 and 2010. The median age of the 4,160 index patients was 72 years old, and 47.6% were male. The patients were identified from the Utah Cancer Registry Population, and data about the relatives were obtained from the Utah Population Database. Population controls not diagnosed with carcinoma of unknown primary were sex and age matched 10:1 to the patients with carcinoma of unknown primary. “Compared to elsewhere, Utah has lower rates of smoking and alcohol use in the population, which could limit generalizability to other populations,” the authors acknowledged.

Adenocarcinoma in More Than One-Third

Among the patients with carcinoma of unknown primary, 36.3% (1,511 patients) had a histologic subtype of adenocarcinoma; 26.4% (1,098 patients) had carcinoma not otherwise specified; 7.8% (326 patients) had squamous cell carcinoma; 5.0% (207 patients) had neuroendocrine tumors; and 24.5% had other types.

First-degree relatives of the patients with carcinoma of unknown primary “were at an elevated risk of carcinoma of unknown primary themselves (hazard ratio [HR], 1.35 [95% confidence interval [CI], 1.07–1.70]), as well as lung (HR, 1.37 [95% CI, 1.22–1.54]), pancreatic (HR, 1.28 [95% CI, 1.06–1.54]), myeloma (HR, 1.28 [95% CI, 1.01–1.62]), and non-Hodgkin lymphoma (HR, 1.16 [95% CI, > 1.00–1.35]) cancers compared with controls without carcinoma of unknown primary,” the researchers reported. “When the analysis was restricted to relatives of cancer-free controls, additional increased risks for colon (HR, 1.19 [95% CI, 1.06–1.33]) and bladder (HR, 1.18 [95% CI, > 1.00–1.38]) cancers were observed. Second-degree relatives of patients with carcinoma of unknown primary were at a slight increased risk of lung (HR, 1.14 [95% CI, 1.03–1.26]), pancreatic (HR, 1.17 [95% CI, 1.01–1.37]), breast (HR, 1.09 [95% CI, 1.02–1.16]), melanoma (HR, 1.09 [95% CI, > 1.00–1.19]), and ovarian (HR, 1.19 [95% CI, 1.02–1.39]) cancers.”

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.


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