Clinical impact of carbonic anhydrase 9 expression on neoadjuvant chemoradiotherapy in pancreatic ductal adenocarcinoma.

Background: PDAC cells upregulate carbonic anhydrase 9 (CA9) expression in order to survive in hypoxic tumor environments, which plays a key role in tumor progression. However, the relationship between CA9 expression and preoperative treatment has not been clarified. We evaluated the clinical impact of CA9 expression on the efficacy of neoadjuvant chemoradiotherapy (NACRT) in pancreatic ductal adenocarcinoma (PDAC).

Methods: We investigated CA9 expression in 273 surgical specimens and 20 serum samples obtained from patients with PDAC and evaluated their clinical outcomes. We analyzed the function of CA9 using human pancreatic cancer cell lines.

Results: CA9 was positively expressed in 36.2 % of patients who underwent NACRT, which was significantly lower than those who underwent upfront surgery (US) (58.9 %, p < 0.001). Interestingly, patients who were CA9-positive in the US group had a significantly poorer prognosis than that of those in the NACRT group (median survival time [MST], 21.5 months vs. 49.2 months, p < 0.001), while there was no significant difference between patients who were CA9-negative in the US and NACRT groups (MST, 45.8 months vs. 46.3 months, p = 0.357). Moreover, serum CA9 levels tended to correlate positively with CA9 expression in cancer tissues. In-vitro experiments demonstrated that CA9 expression was reduced after treatments with radiation and chemoradiation therapy (RT/CRT), and that CA9 knockdown suppressed the impact of RT/CRT on cancer cell proliferation.

Conclusions: CA9 may act as a target molecule for RT/CRT, highlighting its clinical importance as a valuable biomarker for more stringent indications for NACRT.