Peritoneal carcinomatosis (PC) is one manifestation of metastatic CRC and is associated with a poor prognosis [
3]. Few studies have been published describing the effectiveness of systemic chemotherapy in patients with PC. The results invariably show a disappointing response to systemic treatment and a poor prognosis compared to other metastatic sites [
2,
3]. CRC frequently overexpresses EpCAM [
5]. Overexpression of EpCAM has been associated with dismal prognosis in other tumor entities, such as gallbladder cancer, ovarian cancer and pancreatic cancer [
8‐
10]. Catumaxomab, the first anti-EpCAM antibody, was approved in 2009 for the treatment of malignant ascites in cancer patients with EpCAM positive tumors [
6]. This prospective randomized phase II/III trial showed a significantly prolonged median puncture free survival with catumaxomab (46 days) compared to paracentesis alone (11 days) in the pooled population. Although the study was not powered to detect a difference in overall survival, OS showed a positive trend for the catumaxomab group and was significantly prolonged in patients with gastric cancer patients compared to paracentesis alone (71 versus 44 days;p = 0.0313). Interestingely, in our case report treatment with catumaxomab not only extended puncture free survival by 12 months but also caused a regression of the pulmonary metastasis suggesting a possible systemic effect. So far an extraperitoneal effect of catumaxomab has never been described in a patient with colorectal cancer and was reported for a patient with ovarian cancer and breast cancer [
11,
12]. A possible explanation for this systemic effect on tumor cells might be that catumaxomab is absorbed by lymphatics in the peritoneum and reaches the circulation. Low systemic catumaxomab levels (<1%) could be measured after i.p. infusion in nine out of thirteen patients with a high observed inter-individual variability [
13]. Thus, an inverse correlation between tumor burden and systemic antibody bioavailability of catumaxomab was demonstrated in patients and in a defined mouse model [
13]. The bioavailability of catumaxomab significantly declined in mice with higher tumor load. In the pivotal trial of Heiss et al. efficacy of catumaxomab was higher in patients without metastasis compared to patients with higher metastasis [
6]. Therefore, in our patient a lower tumor burden might have resulted in higher plasma levels of catumaxomab. As blood samples have not been taken this determinant remains speculative. Furthermore an induction of anti-tumor specific T-lymphocytes that has been described after intraperitoneal administration of catumaxomab might be causative for its antiproliferative effect on distant metastasis [
14]. Thus, in 5 out of 9 patients intraperitoneal administration of trifunctional antibodies such as catumaxomab induced a significant increase of tumor reactive CD4+/CD8+ T-lymphocytes with a prolonged survival. As catumaxomab is a nonhumanized chimeric antibody derived from mouse/rat IgG it is immunogenic when administered to humans. Thus, the development of human antimouse antibodies (HAMAs), which are associated with beneficial humoral effects and prolonged survival, could be detected in up to 95% of patients treated with catumaxomab [
6]. In a
post hoc analysis the correlation between the detection of HAMAS and clinical outcome was analyzed [
15]. Patients who developed HAMAs after catumaxomab showed significant improvement in puncture-free survival, time to next puncture and OS [
15]. Unaware of the impressive clinical outcome, no blood samples were taken from our patient in order to detect HAMAs. In the study of Heiss et al. the primary study objective was puncture free survival. Additionally the number of intraperitoneal tumor cells was counted before and after intraperitoneal administration of catumaxomab but no imaging method was used to assess the response to catumaxomab [
6]. In the randomized phase IIa study by Baumann et al., response to catumaxomab in patients with platinum-resistant or –refractory epithelial ovarian cancer was assessed according to the Response Evaluation Criteria in Solid Tumors (RECIST) guidelines for the first time [
16]. The study revealed that catumaxomab had only modest activity in platinum-resistant ovarian cancer with an overall response rate of 28% in the high- dose treatment arm (10,20,50 and 100 μg) compared to 5% in the low-dose group (10,10,10 and 10 μg) on days 0,3,7 and 10.
Taken together, our observation suggests that catumaxomab might have a relevant systemic effect on cancer cells and therefore might improve the prognosis of patients with EpCAM-positive tumors. Further investigations to prove and to further explain this systemic effect of catumaxomab are warranted.