Excellent prognosis following endoscopic resection of patients with rectal neuroendocrine tumors despite the frequent presence of lymphovascular invasion.
BACKGROUND
Endoscopic resection (ER) has been increasingly used for the treatment of rectal neuroendocrine tumors (NETs); however, only limited data are available on its long-term outcomes. This study analyzed the long-term outcomes of rectal NETs treated by ER and characterized potential risk factors for metastasis in these cases, with emphasis on lymphovascular invasion.


METHODS
We retrospectively analyzed the clinicopathological features and outcomes of 86 patients with 90 rectal NETs who had been treated by ER. Lymphovascular invasion was reevaluated using elastic-staining and double-staining immunohistochemistry.


RESULTS
En bloc resection with tumor-free margins was achieved in 87 lesions (96.7%). The median tumor size was 5 mm (range 2-13), and all the lesions were confined to the submucosal layer. The Ki-67 index was less than 3% in all the lesions, which were therefore classified as NET G1. Elastic-staining and double-staining immunohistochemistry revealed the presence of lymphatic and venous invasion in 23 (25.6%) and 35 lesions (36.7%), respectively. Collectively, lymphatic and/or vascular invasion was identified in 42 lesions (46.7%). All cases were followed up without additional surgery, and no metastasis or recurrence was detected during the median follow-up period of 67.5 months.


CONCLUSIONS
This study showed an excellent long-term prognosis following ER of patients with rectal NETs, confirming that ER is a valid treatment option for small rectal NETs. The present study also revealed highly prevalent lymphovascular invasion even in minute rectal NETs; this observation raises a question regarding its significance as a risk factor for metastasis.
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan. masekigu@ncc.go.jp.|Advanced Clinical Research of Cancer, Juntendo University Graduate School of Medicine, Tokyo, Japan. masekigu@ncc.go.jp.
Masau
M
Sekiguchi
Pathology and Clinical Laboratory Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan. ssekine@ncc.go.jp.
Shigeki
S
Sekine
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan.
Taku
T
Sakamoto
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan.
Yosuke
Y
Otake
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan.
Takeshi
T
Nakajima
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan.
Takahisa
T
Matsuda
Pathology and Clinical Laboratory Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Hirokazu
H
Taniguchi
Pathology and Clinical Laboratory Division, National Cancer Center Hospital, 5-1-1 Tsukiji, Chuo-ku, Tokyo, 104-0045, Japan.
Ryoji
R
Kushima
Advanced Clinical Research of Cancer, Juntendo University Graduate School of Medicine, Tokyo, Japan.
Yuichiro
Y
Ohe
Endoscopy Division, National Cancer Center Hospital, Tokyo, Japan.
Yutaka
Y
Saito
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001808:Blood Vessels / Q000473:pathology; D016099:Endoscopy, Gastrointestinal / Q000379:methods; D005260:Female; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009389:Neovascularization, Pathologic / Q000473:pathology; D018358:Neuroendocrine Tumors / Q000098:blood supply / Q000473:pathology / Q000556:secondary / Q000601:surgery*; D011379:Prognosis; D012004:Rectal Neoplasms / Q000098:blood supply / Q000473:pathology / Q000601:surgery*; D012189:Retrospective Studies; D016896:Treatment Outcome; D055815:Young Adult
Endoscopic resection; Lymphovascular invasion; Rectal neuroendocrine tumor