Current issues in the treatment of colorectal cancer

Use of brachytherapy in management of locally recurrent rectal cancer

PURPOSE

Locally recurrent rectal cancer is associated with poor quality of life and has justified aggressive surgical and adjuvant approaches to control the disease. This study was designed to evaluate if the use of brachytherapy in association with wide surgical excision (debulking operation) can offer reasonable palliation for patients with locally recurrent rectal cancer.

MATERIALS AND METHODS

Patients with biopsy-proven locally recurrent rectal cancer who were not candidates for intraoperative radiation therapy and who were previously considered as having unresectable tumors were included in the study and were followed-up from May 1981 to November 1990. All of them had undergone laparotomy and had either radical or debulking surgical resection performed. At the same time, brachytherapy was used with temporary or permanent implant of seeds of iridium-192 or iodine-125.

RESULTS

Thirty patients were included. Patients ranged in age from 28 to 74 years, and 16 patients were female. No mortality was observed, and morbidity was low (small-bowel obstruction (1 patient), intestinal fistula (1 patient), and urinary fistula (1 patient). Histologic examination of the specimen showed gross residual disease in 67 percent of patients and microscopic disease in 25 percent of patients. Long-term follow-up was possible in 28 patients. Mean follow-up and local control were, respectively, 26.5 months and 37.5 percent for gross residual disease and 34 months and 66 percent for microscopic residual disease. Eighteen patients (64 percent) had locally recurrent rectal cancer under control at the time of the last follow-up, with seven patients (25 percent) having no evidence of local or distant recurrence.

CONCLUSION

This is the first report of brachytherapy for locally recurrent rectal cancer. This appears to offer a therapeutic alternative to patients who are not candidates for intraoperative radiation therapy. Surgical morbidity and mortality are acceptable. Local control in 18 patients (64 percent) is comparable with intraoperative radiation therapy or more morbid surgical alternatives. Cancer-related deaths are most often related to disseminated disease, which suggests the need for systemic therapy in addition to brachytherapy.

Radiotherapy and hyperthermia

72 patients with either unresectable or pelvic recurrence of colorectal cancer were treated with combined radiotherapy and locoregional hyperthermia. Radiation doses were 50 Gy or more in patients not previously treated with radiotherapy, and 32 Gy (8 x 4 Gy) in patients who had previously received radiotherapy. Hyperthermia was administered within 30 min of irradiation, and the aim was to give four to six sessions once or twice a week, intending to reach temperatures of at least 41 degrees C over 30 min. The mean of all the minimum (TMIN), maximum (TMAX) and median (TMED) intratumoral temperatures were 39.6, 41.1 and 40.2 degrees C, respectively. Toxicity during hyperthermia treatment consisted mainly of local pain within the heated field (33%) and general discomfort (17%). In 17% of the patients, the hyperthermic treatment was prematurely stopped. Palliation was achieved in 75% of patients with a mean duration of 12 months. The percentage of palliated patients was higher when higher radiation doses were administered. No correlation between palliative effect and thermal parameters was found. A computed tomography scan proved objective remission was obtained in 11 patients (15%). Median survival was 11 months, and 17% of the patients were alive at 3 years. The literature on combined radiotherapy and hyperthermia in colorectal cancer is reviewed. From this review and our own data, it is concluded that thermoradiotherapy is feasible. Acute and late toxicity are not major problems, although pain and general discomfort hamper hyperthermic treatment. The most disappointing fact is that, with the available hyperthermia equipment, the increase in intratumoral temperature does not reach, in general, the therapeutic range.

Metabolism of 5-fluorocytosine to 5-fluorouracil in human colorectal tumor cells transduced with the cytosine deaminase gene: significant antitumor effects when only a small percentage of tumor cells express cytosine deaminase

The gene encoding cytosine deaminase (CD) has been expressed in the human colorectal carcinoma cell line WiDr. Metabolism studies confirm that tumor cells expressing CD convert the very nontoxic prodrug 5-fluorocytosine (5FCyt) to 5-fluorouracil (5FUra) and 5FUra metabolites. Tumor xenografts composed of CD-expressing cells can selectively generate tumor levels of > 400 microM 5FUra when the host mouse is dosed with nontoxic levels of 5FCyt. The selective metabolic conversion of 5FCyt to 5FUra in CD-expressing tumor cells results in the inhibition of thymidylate synthase and incorporation of 5FUra into RNA. 5FUra is also liberated into the surrounding environment when CD-expressing tumor cells are treated with 5FCyt. The liberated 5FUra is able to kill neighboring, non-CD-expressing tumor cells in vitro and in vivo. Most importantly, when only 2% of the tumor mass contains CD-expressing cells (98% non-CD-expressing cells), significant regressions in all tumors are observed when the host mouse is dosed with nontoxic levels of 5FCyt.

Adjuvant therapy for adenocarcinoma of the rectum

Surgical resection continues to be the primary curative modality for patients with adenocarcinoma of the rectum. However, local tumor recurrence in the pelvis and/or distant metastasis may occur in spite of complete excision of grossly visible malignant disease. Surgical and pathologic staging can identify a subset of surgically treated rectal cancer patients at high risk for tumor relapse and death. Irradiation and chemotherapy have been used as adjuvant therapy in conjunction with surgery as single modalities and in combination for patients with high risk rectal cancer. Evidence from controlled clinical trials indicates a significant decrease in local tumor recurrence, and a significant improvement in disease-free and overall survival with the use of combined postoperative irradiation and chemotherapy in this setting. A current national clinical trial in the United States of America is studying whether irradiation can be combined with new chemotherapy regimens which have shown significant therapeutic benefit as surgical adjuvant therapy for patients with high risk colon cancer (5FU + levamisole) and for patients with metastatic colorectal cancer (5FU + leucovorin) to further improve the efficacy of surgical adjuvant therapy for adenocarcinoma of the rectum.

Colon, rectum, and anus

Cancer of the colon is the second most common cancer. Adherence to principles of screening, diagnosis, and management have the potential to substantially improve survival.

Detection of metastasis-associated differences for receptors of glycoconjugates (lectins) in histomorphologically unchanged xenotransplants from primary and metastatic lesions of human colon adenocarcinomas

Clinically applicable markers for tumor progression may be uncovered by selective analysis of biochemical parameters, supposedly participating in this complex process. Owing to the importance of specific protein-carbohydrate interactions in diverse biological processes, the pattern of the receptor part in this glycobiochemical recognition system, the sugar receptors (lectins), conceivably reflects biological properties of tumor cells in glycobiochemical terms. Therefore, we established and characterized xenografts from surgically removed specimens of a human primary colon adenocarcinoma and its metastatic lesions to liver of the same patient and of a histomorphologically similar primary colon adenocarcinoma of another patient in nude mice. Xenotransplantation and subsequent glycobiochemical analysis of material from early passages with a standardized procedure had been preferred to cell culture in monolayer on account of maintenance of a higher degree of organized histotypic assembly. Despite histomorphological similarities, the sugar receptor profile revealed significant differences in tumor-tumor and tumor-metastasis comparison, especially for alpha- and beta-galactoside-binding proteins. Tumor-metastasis differences were substantiated by a second successfully xenotransplanted pair of specimens. Comprehensive expansion of these initial data may eventually lead to desirable functional correlations with the different biological properties of histomorphologically similar primary colon adenocarcinomas and of the metastatic phenotype and to a rational development of therapeutic modalities to restrict tumor growth and spread.

Intraoperative and external beam irradiation for locally advanced colorectal cancer

In view of poor local control rates obtained with standard treatment, intraoperative radiation (IORT) using electrons was combined with external beam irradiation and surgical resection, with or without 5-fluorouracil (5FU), in 51 patients with locally advanced colorectal cancer (recurrent, 36 patients; primary, 15 patients). Patients received 4500-5500 cGy (rad) of fractionated, multiple field external beam irradiation and an IORT dose of 1000-2000 cGy. Thirty of 51 patients (59%) are alive and 22 patients (43%) are free of disease. In 44 patients at risk greater than or equal to 1 year, local progression within the IORT field has occurred in 1 of 44 (2%) and within the external beam field in 8 of 44 (18%). All local failures have occurred in patients with recurrence or with gross residual after partial resection, and the risk was less in patients who received 5FU during external irradiation (1 of 11, 9% vs. 6 of 31, 19%). The incidence of distant metastases is high in patients with recurrence, but subsequent peritoneal failures are infrequent. Acute and chronic tolerance have been acceptable, but peripheral nerve appears to be a dose-limiting structure. Randomized trials are needed to determine whether potential gains with IORT are real.

Carcinoma of the rectum: current management

In recent years, various approaches have been used to improve survival and the quality of life in patients after surgical treatment of rectal carcinoma. These approaches include earlier detection, sphincter-saving procedures, and adjuvant therapy, intraoperative therapy for locally advanced tumors, and a more aggressive approach for locally recurrent or distal but isolated spread of the disease.