Study of Blood Samples From Patients With Malignant Melanoma, Metastatic Breast Cancer, Advanced Lung Cancer, Pancreatic Cancer, or Colorectal Cancer.

RATIONALE: Studying samples of blood from patients with cancer in the laboratory may help doctors learn more about changes that occur in peptides and proteins and identify biomarkers related to cancer.
PURPOSE: This research study is looking at blood samples from patients with malignant melanoma, metastatic breast cancer, advanced lung cancer, pancreatic cancer, or colorectal cancer.