CUP is a histologically proven metastatic malignant tumor with a primary site that cannot be identified during pretreatment evaluation [1]. CUP, with its variety of biological characteristics, accounts for 3–5% of all malignancies, approximately 50% of which are diagnosed as well- to moderately differentiated metastatic adenocarcinoma, 30% as undifferentiated or poorly differentiated carcinoma, 15% as SCC and the remaining 5% as undifferentiated neoplasms [2].
A detailed medical history and physical findings are important for diagnosis, followed by various examinations such as blood biochemical tests including tumor markers, chest X-ray and whole-body CT [2, 3]. Furthermore, if tumor tissue can be collected, immunohistochemical staining is necessary for exclusion of occult primaries and for suggesting tissues of origin [4].
CUP remains an extremely aggressive disease with a poor prognosis. The median survival time is between 4 and 12 months [2, 5], and select patients with favorable subsets of CUP have median overall survival times ranging from 12 to 36 months [6]. It is thought that more than half of patients with CUP have multiple lesions [7], and chemotherapy has a main role in the treatment of CUP. Although no regimen has been established as a standard first-line therapy [8, 9], a combination of platinum plus taxane-based chemotherapy obtained a superior response rate and survival in the reported phase II trials [8, 10-12]. However, multiple phase II studies have found no superior combination of cytotoxics, and there remains no standard second-line therapy [9].
Radiation therapy is also an option for localized tumors. In some cases, radical irradiation may be considered, and in others, palliative treatment. In the present case, although it was necessary to begin chemotherapy immediately, there was concern about renal dysfunction due to the left ureteral stenosis. Therefore, a left nephrostomy was performed before chemotherapy to preserve his renal function. Besides, left leg pain due to the tumor was severe, and palliative radiation therapy was started for a total of 10 Gy before the induction of chemotherapy. Furthermore, because radiation monotherapy could also cause metastasis, it was essential that the patient begin early systemic chemotherapy, and he initially underwent combination therapy of weekly paclitaxel plus carboplatin. However, because of the infusion reaction caused by the paclitaxel at the first injection, a different combination regimen of taxane plus platinum was needed. Thus, the patient was administered Bi-DCF chemotherapy [13],, which is used for advanced esophageal squamous cell carcinoma in our institution, after ethics committee approval was received.
A regimen combining docetaxel, cisplatin and 5FU is also used for esophageal cancer, gastric cancer and head and neck cancers, and is also described in the NCCN guidelines. It offers a prolonged prognosis compared to conventional cisplatin plus 5FU combination therapy although there is concern about renal dysfunction [14-17]. Hara et al. also reported that the same regimen was used as preoperative chemotherapy for esophageal cancer, with a response rate of 64%, Grade 3/4 leukopenia of 45% and neutropenia of 83% [18]. In our institution, we performed Bi-DCF therapy as neoadjuvant chemotherapy for esophageal cancer and reported Grade3/4 leukopenia of 12.5%, neutropenia of 31.4%, and no instances of renal dysfunction while maintaining a high response rate of 90.3% compared with previous reports [19]. Bi-DCF therapy can be safely performed even in patients with potential high risk of renal dysfunction such as in this case, and it is thought that high effects can be expected.
Although there is no unified opinion regarding surgical treatment for CUP, it is often considered when a single, resectable tumor is present. If the tumor can be resected without tumor remnants, a favorable prognosis can be expected.
In the present case, tumor shrinkage due to chemotherapy following palliative radiotherapy was obtained and clarified the margin between the tumor and iliac artery, vein and ureter. Therefore, surgical treatment could be performed without tumor remnants although the left external iliac vein was sacrificed because of suspected tumor invasion. Moreover, the resected tissue was fibrous tissue with extensive necrosis without viable cells, and granulation formation and the accumulation of foamy histiocytes were observed. All of these were changes that occurred due to the therapeutic effect after the tumor was reduced in size. The patient has experienced no recurrence or distant metastasis for 4 years.