LAUSR

To the Editor, We read with interest the study entitled, 'Necessity of posttreatment surveillance for low‐grade appendiceal mucinous neoplasms' by Gupta et al., aiming to characterise posttreatment surveillance and determine the risk of recurrence of incidental low‐grade appendiceal mucinous neoplasms (LAMN) following appendicectomy. This study is welcome because the risk factors of progression from LAMN to pseudomyxoma peritonei (PMP) remain poorly understood. The authors retrospectively evaluated 114 patients and found no recurrences after a median 4.7‐year follow‐up. On this basis, they conclude that routine surveillance may be unnecessary in LAMN, regardless of the T‐stage category. In response, we would raise concern regarding the conclusion that surveillance following surgical resection of LAMN may be unnecessary, and advocate the need for shared criteria for selecting follow‐up as a management strategy. Unfortunately, the study population was composed mainly of patients with early Tis tumours, and only 39 (34%) had postoperative surveillance. Among these, there were only 10 pT3/pT4 tumours. In addition, posttreatment surveillance was heterogeneous and included clinical visits (82%), CT (77%) or MR (13%) scans, colonoscopy (38%) and serum tumour markers (31%). Most of these patients probably do not benefit from intensive surveillance. Gupta et al. correctly remind us of the opportunity to avoid any unnecessary investigation with the inherent costs and risks. In our experience, the risk of developing PMP in patients we classify as LAMN‐I (i.e., nonperforated pTis/pT3) is low. Less than 1% of 187 LAMN‐I patients developed peritoneal disease recurrence with a median follow‐up of 25 (1–155) months. We acknowledge with Gupta et al. the lack of highly reliable prognostic factors for LAMN. Although the risk of recurrence is directly related to the degree of tumour infiltration and extra‐ appendiceal spread at the time of diagnosis, some patients develop PMP despite having the early‐stage disease at presentation (Figure 1). However, this low‐risk population appears to be insufficient to describe the natural history of LAMN comprehensively. Patients who have undergone resection for LAMN‐II (perforated/ pT4a/b) have a much higher risk of developing the recurrent disease. The number of patients in Gupta et al.'s study with pT4a and pT4b tumours was only 12 and 1, respectively. In addition, the follow‐up was relatively short (1.9 years for the subgroup who received posttreatment monitoring and 4.7 years for the overall study population), raising the possibility of undetected PMP. In this regard, it would be helpful if the author would also mention the length of the follow‐up for the pT3/pT4 cases. Finally, the follow‐up data of the patients who did not receive any active surveillance was gathered from medical visits and radiological imaging for other conditions, which again raises the possibility of bias. Several studies indicate the risk of PMP following the identification of a LAMN, with incidence rates ranging from 5% to 40%. In a Dutch retrospective study on 545 patients, the rate was 20%—mainly within the first 2 years. The authors recommended performing CT scans for at least 5 years. A similar 26% recurrence rate was reported from the analysis of the MD Anderson database, including 98 patients. Likewise, peritoneal recurrence was detected in 23% of 22 patients monitored with tumour marker, CT scans and exploratory laparoscopy at 12 months. We have developed a protocol applied to all patients referred to our service following the resection of LAMN. This comprises an expert pathological assessment and a baseline oral and IV‐ enhanced CT scan to ensure there is no measurable residual peritoneal disease (i.e., PMP). The strategy is modulated according to tumour characteristics (T‐stage, perforation, presence of extra‐appendiceal mucin with or without neoplastic epithelium). This is in line with the recommendations by the Chicago Consensus Working Group. Accordingly, our patients with LAMN‐I are offered a less intensive schedule, whereas those with LAMN‐ II are offered more intensive follow‐up or laparoscopic risk‐ reducing CRS‐HIPEC, depending on high‐risk features, patient's age, performance status and personal preferences (Table 1). Interestingly, among 55 patients who underwent laparoscopic CRS‐ HIPEC with a normal post appendicectomy CT scan, 36% were found to have residual intraperitoneal mucin (with neoplastic epithelium in 3.6% of cases). With a median follow‐up of 62.5 months, the risk of disease recurrence in 89 LAMN‐II patients who were selected for surveillance was only 1.1%, likely reflecting effective identification of high‐risk clinicopathological characteristics amongst patients who were then selected for laparoscopic risk‐reducing CRS‐HIPEC. In specialist referral centres, patients with advanced PMP arising from LAMNs are not rare, and their number may increase following the COVID‐19 pandemic and its impact on follow‐up schedules. Our experience highlights the importance of specialist