Optimal treatment strategies for clinically suspicious lateral pelvic lymph node metastasis in rectal cancer

Background: Although lateral pelvic lymph node (LPN) metastasis is a major cause of local recurrence in patients with rectal cancer, controversy still remains on the treatment of suspected LPN metastasis, "suspicious LPN". We aimed to determine the optimal treatment strategies for suspicious LPN, in patients with locally advanced rectal cancer who underwent preoperative chemoradiotherapy (CRT). Materials and Methods: Of 377 patients who received preoperative CRT for rectal cancer between 2006 and 2013, 84 (22.3%) had suspicious LPNs on pretreatment MRI. Patients' characteristics, MRI findings, operative and pathologic findings, and oncologic outcomes were analyzed retrospectively. Results: Of 84 patients with suspicious LPNs, 61 showed good response to CRT on posttreatment MRI (short-axis LPN diameter < 5 mm). Among them, 31 patients underwent TME alone (group A), and 30 underwent TME plus LPND (group B). The remaining 23 patients had persistently suspicious LPNs on post-CRT MRI and underwent TME plus LPND (group C). Pathologic LPN metastasis was confirmed in five patients (16.7%) in group B and 15 (62.5%) in group C. Local recurrence developed in 7 (22.6%), 0 (0%), and 4 (17.4%) patients in groups A, B, and C, respectively. Five patients (16.1%) in group A developed in situ LPN recurrences. The 3-year disease-free survival rates were 53.7%, 74.2%, and 46.9% in groups A, B, and C, respectively. Conclusions: Study findings suggested that LPND cannot be omitted for patients with suspicious LPNs on pretreatment MRI even with good response to CRT. Findings from pretreatment MRI should be considered to determine whether LPND is indicated.