Clinical implication and management of rectal cancer with clinically suspicious lateral pelvic lymph node metastasis: A radiation oncologist's perspective

Abstract

Rectal cancer is the eighth most common malignancy worldwide. With the introduction of total mesorectal excision (TME) and neoadjuvant chemoradiation (NCRT), intrapelvic local control has been remarkably improved. However, lateral pelvic recurrence remains problematic, especially in patients with clinically suspicious lateral pelvic lymph node (LPLN). LPLN dissection has been applied for the management of LPLN metastasis, mainly in Japan and other Eastern countries, while the role of NCRT is more emphasized and LPLN dissection is performed in very limited cases in Western countries. However, the optimal management strategy for patients with rectal cancer with suspicious LPLN metastasis has not been determined. Herein, we review the latest studies on the optimal management of LPLN metastasis to suggest the most appropriate treatment policies according to current evidence and discuss future research directions.

Keywords: chemoradiation; lateral pelvic lymph node; lymph node dissection; neoadjuvant treatment; radiotherapy; rectal neoplasm; recurrence.

Figure 1

Examples of rectum anatomy on magnetic resonance image from a man (A) and a woman (B) with rectal cancer. In the National Comprehensive Cancer Network (NCCN) guidelines, the rectum is defined as the portion of the bowel located below an imaginary line drawn from the sacral promontory to the top of the pubic symphysis (white dashed lines). The anterior peritoneal reflections (white arrows) is located around the upper border of the seminal vesicle [asterisk in (A)] in the man or uterocervical angle [asterisk in (B)] in the woman. In the NCCN guidelines, the rectum is divided according to the relative location from the anterior peritoneal reflection: upper rectum, above the anterior peritoneal reflection; mid-rectum, at the anterior peritoneal reflection; and lower-rectum, below the anterior peritoneal reflection. Rectal cancers (black arrows) locate below (A) and across (B) the anterior peritoneal reflection.

Figure 2

Lymphatic drainage of the rectum. The lymphatic drainage above the peritoneal reflection follows mostly an upward pathway along the perirectal, superior rectal, and inferior mesenteric nodes via the mesenteric vessel (along the dark blue arrow). Rectal tumors below the peritoneal reflection tend to drain along the mid-rectal vessel and then into the pelvic sidewall lymph nodes, including the obturator, internal iliac, external iliac, and common iliac lymph nodes (along the sky-blue arrow). The third route of the lymphatic drainage is from the level below the dentate line, in which the lymphatic spread is along the inferior rectal vessel and then into the superficial inguinal and external iliac lymph nodes.

Figure 3

Example of a dosimetry in the radiation therapy (RT) plan with a boost to the lateral pelvic lymph node (LPLN) using the intensity-modulated RT (IMRT) simultaneous intensity boost (SIB) technique. The patient is a 62-year-old woman with non-metastatic locally advanced rectal adenocarcinoma extending to the lower rectum with perirectal fat invasion and clinically suspicious LPLN metastases in the left internal iliac and right obturator area. The LPLNs are irradiated with 58.8 Gy in 28 fractions [red color washes in (A-C)] while the primary tumor [orange lines in (A-C)] and other lymphatic area [sky-blue lines in (A-C)] were irradiated with 50.4 Gy in 28 fractions. (D) shows the dose-volume histogram of the RT plan (yellow line, bladder; purple line, right femur head; violet line, left femur head; orange line, primary tumor, sky-blue line, pelvic lymphatics; pink line, LPLNs).