Clinical importance of suspicious for malignancy compared to positive for malignancy in peritoneal cytology for surgically resected pancreatic cancer.

Background/objectives: Positive peritoneal cytology (Cy+) is considered a form of microscopic dissemination and a poor prognostic factor in resected pancreatic cancer (PC). However, the clinical implications of equivocal categories such as atypia of undetermined significance (AUS) and suspicious for malignancy (SFM) remain unclear.

Methods: We retrospectively analyzed patients with PC who underwent surgery at 13 high-volume centers between January 2009 and December 2018. Inclusion criteria were: 1) cytology results of AUS, SFM, or malignant (MAL); 2) resectable (R) or borderline resectable (BR); 3) no other macroscopic metastases; and 4) no preoperative therapy.

Results: A total of 239 cases were included (AUS: 58, SFM: 31, MAL: 150), with R/BR = 196/43. Survival curves for SFM closely resembled those for MAL but differed from AUS. Grouped analysis showed that SFM + MAL patients had significantly shorter median overall survival (OS) than AUS patients (19.6 vs. 28.0 months, HR 1.61, P < 0.01) and shorter recurrence-free survival (RFS: 8.0 vs. 12.7 months, HR 1.53, P = 0.01). This trend persisted in resectable cases (OS: 21.1 vs. 30.5 months, HR 1.74; RFS: 9.1 vs. 14.2 months, HR 1.57; all P < 0.01).

Conclusions: The cytology of SFM in PC is associated with a prognosis comparable to that of MAL, suggesting the need for cautious clinical interpretation and potential reclassification.