Is detection of intraperitoneal exfoliated tumor cells after surgical resection of rectal cancer a prognostic factor of survival?

Abstract

Background: The prognostic significance of free cancer cells detected in peritoneal fluid at the time of rectal surgery remains unclear. A substantial number of patients will develop metastatic disease even with successful local treatment. This prospective non-randomized study investigated the prognostic value of intraperitoneal free cancer cells harvested in peritoneal lavage after surgery for rectal cancer. Mutational hotspots in mitochondrial DNA were examined as potential molecular signatures to detect circulating intraperitoneal free cancer cells when present in primary tumor and in lavage.

Methods: Point mutations in mitochondrial DNA amplifications were determined in primary tumors and corresponding exfoliated intraperitoneal free cancer cells in lavage from 191 patients with locally advanced rectal cancer scheduled for radical treatment. Mitochondrial DNA target sequences were amplified by polymerase chain reaction and base substitutions were detected by denaturant, cycling temperature capillary electrophoresis. Detection of intraperitoneal free cancer cells was correlated to survival.

Results: Of 191patients analyzed, 138 (72%) were identified with somatic mitochondrial point mutations in rectal cancer tumors. From this fraction, 45 patients (33%) had positive lavage fluid with corresponding somatic mtDNA point mutations in lavage representing circulating intraperitoneal free cancer cells. There was no significant survival difference between patients identified with or without somatic mitochondrial DNA point mutations in the corresponding lavage.

Conclusion: Somatic mitochondrial DNA point mutations identified in primary rectal tumors enable detection of circulating intraperitoneal free cancer cells in lavage fluid. Intraperitoneal free cancer cells harvested from lavage immediately after surgery for rectal cancer does not represent an independent prognostic factor on survival.

Keywords: Prognostic factor; Rectal cancer; Survival; mtDNA mutations.

Fig. 1

Electropherogram of primary rectal tumor without mtDNA mutations (top) and primary rectal tumor with mtDNA mutations (lower)

Fig. 2

Electropherograms of mutant positive primary rectal tumor with mtDNA mutations and in corresponding lavage A & B

Fig. 3

Electropherograms of primary rectal tumor with mtDNA mutations and mtDNA mutations in lavage A, but not in lavage B

Fig. 4

Electropherograms of primary rectal tumor with mtDNA mutations and without mtDNA mutations in lavage A, but with mutation in lavage B

Fig. 5

Kaplan-Meier plot. Survival analysis, calculated from patients with locally advanced and locally recurrent rectal cancer, having positive IPCC or negative IPCC. No censored data

Fig. 6

Kaplan-Meier plot. Survival analysis, calculated from patients with KRAS mutations positive vs. KRAS mutations negative in lavage fluid. No censored data (P = 0,177)