Synchronous Collision Neuroendocrine Tumor and Rectal Adenocarcinoma: a Case Report

Abstract

Collision tumors are thought to arise from the accidental meeting of two independent tumors. Adenocarcinoma is the most common malignant rectal tumor, while neuroendocrine tumor (NET) is relatively rare. Due to the endoscopy and reporting, the overall incidence of NETs was increasing recently but still less than 1 per 100,000. This means that a combination of an adenocarcinoma and NET is a very rare finding and an actual collision of these tumors even more so. We report here a highly unusual case of a 64-year-old woman who had collision tumors composed of a primary rectal adenocarcinoma and NET showing a “side by side” pattern. Resection margins are free of both the tumors. The postoperative course was uneventful. The patient underwent a protocol CT scan at 3 months after surgery, which did not show any recurrence. Both the malignant adenocarcinoma and the NET would make a great influence in the rest lifetime and a follow up will be continued, although the CT did not show any recurrence until now. To the best of our knowledge, this is the first reported case of such an occurrence.

Introduction

Collision tumors are thought to arise from the accidental meeting of two independent tumors. Adenocarcinoma is the most common malignant rectal tumor, while neuroendocrine tumor (NET) is relatively rare. Due to the endoscopy and reporting, the overall incidence of NETs was increasing recently but still less than 1 per 100,000 [1]. This means that a combination of an adenocarcinoma and NET is a very rare finding and an actual collision of these tumors even more so. We report here a highly unusual collision tumors composed of a primary rectal adenocarcinoma and NET showing a “side by side” pattern.

Report of a Case

A 64-year-old woman presented with a change in bowel habits for 11 months with hematochezia for 9 months. Physical examination revealed an infiltrating lesion in the posterior rectal wall. Biopsy provided the histological diagnosis of a moderately differentiated adenocarcinoma. Neoadjuvant chemoradiotherapy introduced firstly oral capecitabine (825 mg/m², twice daily for 5 days/week for 25 days) with a total radiation dose of 50 Gy. Four weeks after chemoradiotherapy, the patient showed a little relief from the initial symptoms, but contrast enema confirmed the lesion persisted (Fig. 1b). CT revealed the absence of liver metastases and other intra-abdominal pathologic processes, but the local incrassated rectal wall and the mass were obvious (Fig. 1a). Magnetic resonance imaging (MRI) provided diagnosis of the invasion of the muscularis propria (Fig. 1c, d). The second colonoscopy was done more carefully and revealed a smooth, round sessile polyp close to the strictured rectal cancer (Fig. 2a, b).

Fig. 1.

Bladder (B), uterus (U), femur (F). a Computed tomography revealed the local incrassated rectal wall and the obvious mass. b Barium enema demonstrated an “apple core” or “napkin ring” lesion caused by a constricting carcinoma. c, d Magnetic resonance imaging provided diagnosis of the invasion of the muscularis propria

Fig. 2.

a Endoscopic view of a smooth, round sessile polyp. b The strictured rectal cancer covering edema and bleeding mucosa. c Heteromorphous cells with nesting patterns. d Moderately differentiated adenocarcinoma

So, low anterior resection of the rectum with regional lymph node dissection was performed for the adenocarcinoma. The resected rectum revealed an ulcerative mass measuring 3 × 2 × 1.3 cm in greatest dimension and a node about 1.2 cm diameter in the anal side, which was about 3 cm away from the ulcerative mass. Microscopically, the ulcerative mass showed a component of moderately differentiated adenocarcinoma (Fig. 2d) as before invading into the muscularis propria of the rectum. The smaller presented heteromorphous cells with nesting patterns (Fig. 2c) and was diagnosed as a grade 1 neuroendocrine tumor based on immunohistochemical results (Ki67 < 2 %, cytokeratin (+), synaptophysin (+), chromogranin A (−)). All 12 resected lymph nodes were free of both adenocarcinoma and NET. Resection margins are free of both the tumors. The postoperative course was uneventful. The patient underwent a protocol CT scan at 3 months after surgery, which did not show any recurrence.

Discussion

The term collision tumors refer to two morphologically different neighboring but independent tumors. Unequivocal collision tumors are rare to find and should be differentiated from mixed or composite tumors. Collision tumors are considered as tumors showing a “side by side” or “one upon another” pattern. They can occur within the same organ but not intermingle, or in adjacent organs, or in conjunction with systemic malignancy [2]. In this case, two morphologically different tumors in continuity by an accidental “meeting” may be the mechanism.

NET of the rectum is rare, comprising less than 1 % of all colorectal malignancies [1]. The clinical presentation of NET varies, depending on the size, the primary site, and the type of substance produced by the tumor. Most rectal NET is small (<1–2 cm) and submucosal. In most cases, the disease is localized [3], but it has become apparent that these supposedly benign tumors may not always behave in such a fashion. Distant metastases may still be present. At present, surgery is the only curative treatment for NET, as the NET’s response to chemotherapy has been traditionally poor [4]. Although NET generally has a better prognosis than adenocarcinomas at the same site, NET is incurable once they advance to unresectable metastatic disease [5]. At the same time, even if these patients are cured of NET, they still have a significant chance of developing a second cancer [6]. This second lesion could develop in sites not only in the rectum but also in all of the sites at risk including the lungs, prostate, and urinary system. Thus, comprehensive and well-documented history and physical examination must be performed at the time the NET is diagnosed [7].

In our case, the special collision tumors accrued and negative margins were done. However, the recurrence and de novo malignancy would mostly be determined by the NET for the previous studies showing a high association of second primary malignancies with G1 NET [6]. Therefore, a vigilant follow-up and surveillance is necessary not only in the colon and rectum but also in all of the sites at risk.

In conclusion, we present a patient suffering from collision tumors consisting of a rectal adenocarcinoma and a G1 NET. Both the adenocarcinoma and the NET would make a great influence in the rest lifetime and a follow up will be continued, although the CT did not show any recurrence until now.