Prognosis

The prognosis for patients with adenocarcinoma of unknown primary site (ACUP) remains poor. Appropriate supportive care should be implemented for all patients with ACUP, to manage both disease-related and treatment-related complications.

Among a cohort of patients in Ontario, 3-year survival for those with adenocarcinoma was substantially poorer compared with that of patients diagnosed with squamous cell carcinoma of unknown primary (3.5% vs. 41.6%, respectively).[50]​ One population-based analysis (using data from the Swedish cancer registry) reported 12-month survival of 41% and median survival 8 months when adenocarcinoma metastases were limited to lymph nodes.[6]​ For patients with extranodal ACUP, 12-month survival was 17%, with median survival of 3 months.[6]

When all cancers of unknown primary (CUP) are considered, average survival time is about 9-12 months after diagnosis.[51]​ Patient information from the Surveillance, Epidemiology and End Results (SEER) registry indicates that, among adolescents and young adults (15-39 years) with a diagnosis of CUP, median overall survival is 11 months, with squamous CUP having the longest median overall survival (16 years).[52]​ SEER data for older adult patients (≥66 years of age) diagnosed with CUP (between 2013 and 2015) suggest a median overall survival of 1.2 months.[53]

For men and women diagnosed with CUP (between 2012 and 2016) in England, estimated 1- and 3-year survival was 16% and 10%, respectively.[54]

Specific prognostic features

By definition, patients who receive site-specific treatment tailored to the presumed primary site have a more favorable prognosis.

The following adverse prognostic factors have been identified:​[2][3][34]​​​​​

  • Unfavorable CUP subtype

  • Adenocarcinoma histology

  • Male sex

  • Older age (≥65 years)

  • History of smoking (more than 10 pack-years)

  • Poor performance status

  • Multiple comorbidities

  • Metastases involving multiple organs (eg, liver, lung, bone), peritoneal metastases, multiple cerebral metastases

  • Nonpapillary malignant ascites (adenocarcinoma)

  • Adenocarcinoma with multiple lung/pleural or bone lesions

Significant independent adverse laboratory parameters include:[3][34]

  • Elevated alkaline phosphatase

  • Elevated lactate dehydrogenase (LDH)

  • Low serum albumin and lymphopenia

  • Elevated neutrophil versus lymphocyte ratio (indicative of an inflammatory state)

Clinical risk score

The Eastern Cooperative Oncology Group performance status (ECOG PS), combined with serum LDH at diagnosis, has been recommended.[3] ECOG PS 0 or 1 and normal LDH indicates good prognosis; PS >1 or elevated LDH confers poor prognosis.

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