Comparison of the comet assay and the oxygen microelectrode for measuring tumor oxygenation in head-and-neck cancer patients.
OBJECTIVE
To compare the Eppendorf PO2 histograph and the alkaline comet assay as methods of measuring tumor hypoxia in patients with head-and-neck squamous cell carcinomas.


METHODS
As part of a larger clinical trial, 65 patients with head-and-neck squamous cell carcinoma nodal metastasis underwent tumor oxygenation measurements with Eppendorf PO2 histographs and comet assays, performed on fine-needle aspirates at 1 and 2 min after 5 Gy. Fifty-four patients had sufficient tumor cells for comet analysis at 1 min and 26 at both 1 and 2 min. Individual cells were examined for DNA single-strand breaks by alkaline gel electrophoresis, and the distribution of values was quantified using median tail moment (MTM). Nonirradiated tumor cells from pretreatment fine-needle aspirates received 5 Gy in vitro to establish the oxygenated response.


RESULTS
There was a significant correlation between the 1- and 2-min MTM (slope = 0.77 +/- 0.03). There was no relationship between DNA damage in tumor cells irradiated in vitro and in vivo. No correlation was found between Eppendorf PO2 measurements and comet MTM. There was a statistically significant correlation between the treatment response in the node studied and comet MTMs, whereas no correlation was observed between treatment response and Eppendorf measurements.


CONCLUSIONS
Comet assays are reproducible, as shown by biopsies at 1 and 2 min. Intertumor variation in the MTM is not a result of intrinsic radiosensitivity but of tumor hypoxia. There was no correlation between Eppendorf PO2 measurements and comet MTM. Comet assays were better than Eppendorf in predicting treatment response as an end point for short-term outcome. Longer follow-up is needed to determine the role of the comet assay as a predictor for locoregional tumor control and survivals.
Department of Radiation Oncology, Stanford University, Stanford, CA 94305, USA. Qle@reyes.stanford.edu
Quynh-Thu
QT
Le
Mary S
MS
Kovacs
Mary Jo
MJ
Dorie
Albert
A
Koong
David J
DJ
Terris
Harlan A
HA
Pinto
Don R
DR
Goffinet
Kent
K
Nowels
Dan
D
Bloch
J Martin
JM
Brown
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy / Q000503:physiopathology* / Q000532:radiotherapy; D015687:Cell Hypoxia; D002945:Cisplatin / Q000008:administration & dosage; D020552:Comet Assay; D004249:DNA Damage; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage; D006258:Head and Neck Neoplasms / Q000188:drug therapy / Q000503:physiopathology* / Q000532:radiotherapy; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D010100:Oxygen / Q000032:analysis*; D011838:Radiation-Sensitizing Agents / Q000627:therapeutic use; D000077704:Tirapazamine; D014227:Triazines / Q000627:therapeutic use
D011838:Radiation-Sensitizing Agents; D014227:Triazines; D000077704:Tirapazamine; D002945:Cisplatin; D010100:Oxygen; D005472:Fluorouracil