RATIONALE: Studying samples of tumor tissue from patients with cancer in the laboratory may help doctors identify and learn more about biomarkers related to cancer.

PURPOSE: This laboratory study is collecting skin biopsy specimens from patients receiving irinotecan or gemcitabine for advanced solid tumors and using them to study change in DNA due to this treatment.

OBJECTIVES:

Primary

• Determine the level of p-Chk1 and phospho-histone 2AX (p-H2AX), an indicator of DNA damage, and possibly downstream pathway markers in hair follicles from skin biopsies of patients treated with gemcitabine hydrochloride or irinotecan hydrochloride for advanced solid tumors.

Secondary

• Characterize the method for measurement (immunohistochemistry).
• Measure inter- and intra-patient variability for the biomarker.
• Partially characterize the dynamic time course of p-Chk1 and p-H2AX after administration of a DNA-damaging agent.

OUTLINE: This is a multicenter study.

Patients undergo collection of 2 skin biopsies with hair follicles at 4 and 8 hours or at 4 and 6 hours after the start of irinotecan hydrochloride or gemcitabine hydrochloride treatment on day 1 of course 1. Repeat biopsies will be taken at 4, 6, or 8 hours after the start of irinotecan hydrochloride or gemcitabine hydrochloride on day 1 of 2 successive courses.

Tissue is examined by immunohistochemistry and possibly other methods for changes in p-Chk1 and pH2AX.

PROJECTED ACCRUAL: A total of 60 patients will be accrued for this study.

DISEASE CHARACTERISTICS:

• Diagnosis of advanced solid tumor malignancy (preferably colorectal, pancreatic, or breast cancer)
• Scheduled to receive a standard dose, weekly regimen of either irinotecan hydrochloride or gemcitabine hydrochloride

PATIENT CHARACTERISTICS:

• Not specified

PRIOR CONCURRENT THERAPY:

• No DNA-damaging agent within the past 13 days