Primary adenocarcinoma of the appendix is a rare malignancy of the gastrointestinal tract[
1]. Smeenk et al[
6] reported a 0.3% prevalence of primary appendiceal mucinous epithelial neoplasms identified from 167 744 patients who underwent appendectomy. Our 18-year-experience showed a similar incidence rate (0.4%) of primary appendiceal carcinoma after appendectomy. Moreover, a primary signet ring cell carcinoma of the appendix (the case reported herein, was the first of the 15 cases) is an exceedingly rare entity, comprising only 4% of all appendiceal neoplasms[
2].
The demographic characteristics of patients with cancer of the appendix vary by histology. According to report of McCusker et al[
1], those diagnosed with malignant carcinoids are significantly younger (mean age, 38 years) than those diagnosed with any of the other cancer types. The mean age of patients at diagnosis of mucinous adenocarcinoma, colonic type adenocarcinoma, and signet ring cell carcinoma is approximately 60 years, 62 years, and 58 years, respectively, and an equal number of males and females developed goblet cell carcinoid, mucinous adenocarcinoma, and signet ring cell carcinoma, except for colonic adenocarcinoma which had a male predominance[
1]. Our results also showed similar demographic findings.
Reported series of appendiceal adenocarcinoma are difficult to compare, as terminology and classification of these lesions are not consistent[
7,8]. The International Classification of Diseases for Oncology (ICD-O) divides the tumors of appendix into five categories: colonic type adenocarcinoma, mucinous adenocarcinoma, signet ring cell carcinoma, goblet cell carcinoma, and malignant carcinoid/adenocarcinoid[
1,9]. These carcinomas arise in pre-existing adenomas, either by a cystic and colonic growth pattern[
10,11]. On the other hand, signet ring cell carcinomas, usually frequent in stomach and intestine, are adenocarcinomas with mucus-producing tumor cells. In this case, the tumor cells showed diffuse, strong immunoreactivity against cytokeratin 20, CDX-2, MUC-2, and CEA, and focal immunopositivity for MUC-5AC (Figure ). CDX-2 is a useful marker to confirm an appendiceal origin of pseudomyxoma peritonei, particularly when used in conjunction with CK20, MUC-2, and MUC-5AC[
12].
Most appendiceal cancers are low-grade neoplasms that are typically relatively indolent. The overall 5-year survival rate for mucinous appendiceal adenocarcinomas reported by Park et al[
13] is 20.5%. According to report of McCusker[
1], except for signet ring cell carcinoma and malignant carcinoid, the histologic type does not have a significant impact on survival. In addition, the extent of disease at diagnosis is a more important predictor of survival than histology. Ronnett et al[
7,14] reported that the long-term survival of patients with diffuse, peritoneal metastases arising from these carcinomas is poor, with a reported 5-year survival as low as 6.7%-14%. Moreover, in a study by McGory et al[
2], poorly differentiated adenocarcinoma and signet ring cell carcinoma of the appendix had the highest proportion of distant disease with a 5-year survival rate of 7%. Therefore, signet ring cell carcinoma may be a separate tumor type in the appendix that should be considered apart from other carcinomas, largely because of its poor prognosis.
Right hemicolectomy is considered the optimal treatment for most histologic types of primary appendiceal carcinoma even in the presence of perforation and in Dukes A tumors[
15]. The treatment options for metastatic disease include systemic chemotherapy alone, hyperthermic intraoperative intraperitoneal chemotherapy, cytoreductive surgery with peritonectomy, and combination of treatments. Of those treatment options, cytoreductive surgery and hyperthermic intraperitoneal chemotherapy have recently become the treatment of choice for metastatic diseases at most large centers[
16]. In the present case, laparoscopic exploration allowed assessment of the pelvic metastasis which was unresectable and the final pathologic diagnosis was a signet ring cell carcinoma, with aggressive biologic behaviors. Therefore, we did not perform cytoreduction or intraperitoneal chemotherapy, but proceeded with an appendicectomy and bilateral salpingo-oophorectomy followed by systemic chemotherapy. Routine oophorectomy should be considered in all females, especially if post-menopausal. An oophorectomy itself may assist with tumour staging, reduce the likelihood of symptomatic metastases and also provide a survival advantage[
17].
Given the predilection for exclusive peritoneal metastasis of mucinous adenocarcinomas of the appendix, in the case of low-grade tumors, cytoreductive surgery and regional chemotherapy are very important. Aggressive cytoreductive surgery for mucinous-type tumours is known to improve the survival rate and reduce the recurrence rate in patients with generalized pseudomyxoma peritonei compared with simple appendectomy[
18]. In addition, the most consistent prognostic factor for survival is the completeness of cytoreduction[
19,20]. However, whether debulking surgery for all patients with aggressive, advanced disease is worthwhile has not been elucidated. In fact, only limited data are available on surgical debulking for diffuse, peritoneal dissemination from aggressive appendiceal carcinomas, in part because the disease is so rare. Incomplete cytoreduction plus perioperative intraperitoneal chemotherapy for peritoneal dissemination from aggressive appendiceal malignancies can achieve a limited long-term survival[
5,20]. Furthermore, Gonzalez-Moreno and Sugarbaker demonstrated that right hemicolectomy does not confer a survival advantage in patients with mucinous appendiceal tumors with peritoneal seeding[
21]. These data suggest that in patients with aggressive appendiceal malignancy, routine right hemicolectomy should not be performed unless in conjunction with complete cytoreduction in combination with intraperitoneal chemotherapy.
Considering systemic chemotherapy, an alternative option to metastatic appendiceal carcinomas, although limited, the available data favor integration of systemic chemotherapy, including mitomycin C, fluoropyrimidines and platinum compounds, which has been used as an intraperitoneal chemotherapy[
20,22]. Ishibashi et al[
22] described a case of pseudomyxoma peritonei caused by carcinoma of the appendix, which was successfully treated with multidisciplinary treatment, including oxaliplatin, 5-FU, and leucovorin (modified FOLFOX6 regimen) combination systemic chemotherapy followed by cytoreduction. In a recent randomized phase III trial comparing debulking alone to debulking with continuous hyperthermic peritoneal perfusion of cisplatin in patients with low-grade, mucinous tumors of the gastrointestinal tract, all patients who had surgical debulking received four courses of postoperative intravenous chemotherapy (5-FU, leucovorin, and oxaliplatin)[
23].
Recently, many targeted drugs have been used as a combination therapy to improve the survival of patients with gastrointestinal malignancies[
24]. Mucin genes, which play an important role in the pathogenesis of pseudomyxoma peritonei, are regulated in part by epidermal growth factor receptor (EGFR) signaling[
25,26]. Andreopoulou et al[
27] recently presented that heavily pretreated patients who underwent cetuximab monotherapy showed a transient decrease in tumor markers, with an encouraging time-to-progression (3 mo) in a phase II trial of cetuximab in mucinous peritoneal carcinomatosis. In addition, Logan-Collins et al[
28] demonstrated that in patients who undergo cytoreductive surgery and intraperitoneal hyperthermic perfusion for mucinous adenocarcinoma of the appendix, (
n = 32), the average vascular endothelial growth factor (VEGF) counts correlate with survival (
P = 0.017), and for patients with recurrence, this correlation is stronger (
P = 0.002), indicating that VEGF may predict the survival of patients with peritoneal surface metastases from mucinous adenocarcinomas and that anti-angiogenic therapies may be effective in patients with this devastating disease. In the future, novel targeted therapies, including EGFR inhibitor or anti-angiogenic agents, in combination with regional treatment or systemic chemotherapy should be evaluated.