title: Survival of patients with visceral metastatic melanoma from an occult primary lesion: a retrospective matched cohort study.
abstract: BACKGROUND
  Malignant melanoma presents as metastatic disease without an apparent primary in about 4% of cases. These are referred to as occult primary melanoma (OPM). It is not known whether these represent de novo malignant transformation in non-cutaneous sites or the disappearance of an unrecognised primary, perhaps on an immunological basis. We hypothesised that OPM might have a superior prognosis compared to patients with similar disease extent from a known primary lesion (KPM).
  
  
  METHODS
  We performed a retrospective cohort survival study of 146 patients with OPM and visceral metastases treated at the Sydney Melanoma Unit between 1983 and 1996. A control group of patients with KPM was matched for age, sex and site of visceral metastases. Survival was measured from the date of diagnosis of visceral metastases.
  
  
  RESULTS
  Patients with OPM had a median survival of 233 days, significantly longer than the 176 days for those with KPM (P = 0.024; logrank test). Multivariate analysis allowing for simultaneous or prior involvement of lymph nodes, subcutaneous tissues or bone, and site of visceral involvement showed a significantly superior survival for OPM (hazard ratio (HR): 0.72; 95% confidence interval (CI): 0.55-0.93). A small part of the effect was explained by treatment, but models allowing for this still showed a significantly longer survival.
  
  
  CONCLUSIONS
  Survival was longer in OPM patients. This may reflect an intrinsically superior host-tumour interaction.
authors.affiliation: Sydney Melanoma Unit, Royal Prince Alfred Hospital, Australia.
authors.forename: G
authors.initials: G
authors.lastname: Vijuk
authors.forename: A S
authors.initials: AS
authors.lastname: Coates
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001859:Bone Neoplasms / Q000556:secondary; D001932:Brain Neoplasms / Q000556:secondary; D016022:Case-Control Studies; D015331:Cohort Studies; D016001:Confidence Intervals; D004067:Digestive System Neoplasms / Q000556:secondary; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008545:Melanoma / Q000401:mortality* / Q000556:secondary*; D008875:Middle Aged; D015999:Multivariate Analysis; D009382:Neoplasms, Unknown Primary / Q000401:mortality*; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012878:Skin Neoplasms / Q000556:secondary; D016019:Survival Analysis