These findings suggest that patients presenting with small (≤1.0 cm) rectal carcinoid tumors in the absence of regional or distant metastases are unlikely to develop local recurrence or metastases after resection. No recurrences were observed in this cohort after a mean follow-up of 5.4 years. This finding coincides with multiple previous studies which have reported no recurrences after resection of tumors ≤1.0 cm, over a median follow-up period of up to 6.4 years and a cohort as large as 84 patients [13
]. Alternatively, Kwaan et al. reported 2 of 48 patients (4%) with a rectal carcinoid tumor <1.0 cm had distant metastatic recurrence discovered at 5 and 13 years after resection [12
]. The initial management and follow-up surveillance of these 2 patients is unclear. The authors’ concluded that their standard surveillance schedule for “high risk” tumors includes proctoscopy every 6 months for 2 years and then annually for 5 years after resection. They further state that patients with “higher risk” tumors should undergo additional endoscopic ultrasonography or rectal magnetic resonance imaging (MRI) in conjunction with octreotide imaging annually for 3 years. These terms of risk were not specifically defined, nor were differences in management stratified based on tumor size.
In 2008, the European Neuroendocrine Tumor Society (ENETS) released a consensus statement on the recommended surveillance of patients following resection of carcinoid tumors of the colon and rectum [18
]. They concluded that tumors <1.0 cm and without LN involvement required no follow-up, whereas tumors 1.0–2.0 cm should be followed if they contained adverse features such as angioinvasion, invasion into muscularis, or atypical histopathology. Tumors >2 cm always required follow-up. Specific surveillance guidelines for tumors without adverse features (i.e. low-risk) include one scan (e.g. rectal EUS, colonoscopy, or MRI) or serum marker (CgA or acid phosphatase if positive pre-resection) within the first year. For high-risk tumors patients should have a scan or serum marker every 4–6 months in the first year and then at least annually. Follow-up is typically for 10 years, although the authors cautioned that metastatic disease can occasionally occur after this period.
There was no consistent follow-up schedule used by physicians in this study. Endoscopy was the surveillance method of choice, whereas other imaging modalities and laboratory measurements were not regularly obtained. If imaging studies were performed on a patient after resection, it was due to symptoms of abdominal or back pain. Given that no recurrences were observed in this American cohort, we concur with the ENETS guidelines that patients with tumors <1.0 cm and without regional or distant metastases are unlikely to need scheduled follow-up after rectal carcinoid resection. This includes surveillance endoscopies and other imaging studies (e.g. EUS, CT, MRI, 111In-octreotide scans). We are unable to make broad recommendations on tumors 1.0 cm in diameter, as only 1 patient in our series met this criterion. However, this particular patient had negative margins achieved on TAE, and was closely followed with 5 repeat endoscopies over 11.3 years with no evidence of recurrence.
It is clear from our study that not all physicians felt it necessary to obtain negative margins. In our series, margin clearance was achieved in only 9 patients (50%), including 5 of 13 patients (38%) treated with endoscopy alone. Consequently, 9 patients (50%) were ultimately left with a positive or indeterminate margin. Despite this, no recurrences of local or distant disease were observed. There are no large series detailing R0 versus R1 recurrences, and the necessity of achieving microscopically negative margins has been questioned in the past [6
]. However, the current consensus is that resection with microscopically negative margins should be done if possible [6
]. This is due to the fact that resection offers the only chance of a cure, and also these tumors can evolve over a long period of time and late recurrences are difficult to capture in the literature [12
Interestingly, despite the discrepancy in final margin status between patients treated surgically versus endoscopically, there was no significant difference in the number of follow-up endoscopies after resection. Although patients who underwent TAE or TEM and had margin clearance underwent a greater number of follow-up endoscopies after resection than patients who were managed endoscopically, the longer length of follow-up in the surgical group likely accounts for this difference. Additional investigation is necessary to detail any potential differences in follow-up practices between surgeons and gastroenterologists, or variations in surveillance in the setting of a negative versus positive margin.
The major limitation of this study is the retrospective method of data collection. Additionally, because the majority of carcinoid tumors were discovered incidentally, common laboratory markers (CgA, 5-HIAA) were not regularly obtained and thus not used as a surveillance modality. Furthermore, histopathologic information (LVI or mitotic rate) demonstrated to affect prognosis and, theoretically, recurrence of rectal carcinoid tumors was not consistently reported. However, because none of our patients recurred, our inability to distinguish between aggressive and non-aggressive tumor types did not effect the conclusions of the study. Lastly, the small sample size and limited length of follow-up make it difficult to draw broad conclusions on follow-up recommendations. As mentioned previously, there have been reported recurrences of small rectal carcinoids 13 years after resection, albeit exceedingly rare. The implications of these uncommon recurrences on the follow-up regimen of the entire population of patients with rectal carcinoid tumors have not been established. Further investigation with larger cohorts and longer follow-up periods is warranted to determine accurate recurrence rates of small rectal carcinoid tumors, and the timing of recurrence.
To our knowledge, there has not yet been a study dedicated to establishing guidelines for surveillance of small rectal carcinoid tumors after resection in the United States, and this study highlights the need for standardization. The long-term behavior of small (≤1.0 cm), non-metastatic rectal carcinoid tumors characterized in this study suggests that recurrence after endoscopic or surgical resection is low or absent. Therefore, a risk-benefit analysis examining the need for scheduled follow-up is essential, primarily because aggressive surveillance with repeat endoscopies or other imaging studies may be unnecessary in this patient population.