INVESTIGATION OF THE ANTI-NEOPLASTIC EFFECT OF TRISHUL (AYURVEDIC AGENT) ON TUMOUR REGRESSION OF RECTAL CANCER- A PILOT STUDY

Introduction

Colorectal cancer is now the third-most common cancer in the world and the second-most common cause of cancer death (1). In Sri Lanka, in 2008, colorectal cancer was the 7th most-common cancer (2); in 2021, colorectal cancer had risen in order to be the third-most frequently occurring cancer in Sri Lanka (3,4).

The rectum is the most frequent site of occurrence of cancer and may be found in up to 60percent of Sri Lankan patients with colorectal cancer (2). Treatment of rectal cancer has evolved over the years from complete removal of the rectum with tumour and the anal canal with its sphincters resulting in a permanent colostomy in the 1950s (5), to preservation of the anal canal and the anal sphincter complex resulting in the ability to restore intestinal continuity and avoid a permanent colostomy since the latter part of the 1990s (6,7). Following surgical resection of rectal cancer by anterior or low anterior resection, and restoration of intestinal continuity, the majority of patients experienced impaired continence and soiling which took up to 2 years to improve (8). A lesser proportion of patients, however, were left with long-term soiling that required the use of a protective garment such as a pad. Despite these disadvantages, for South Asian patients, an operation for rectal cancer that restored intestinal continuity and avoided a permanent stoma was encouraging because of the social taboos that were, and are still, associated with a permanent colostomy, and the cost of stoma appliances (9,10).

Local recurrence of rectal cancer following curative surgical resection remained a problem following seemingly surgical successful treatment of patients with rectal cancer that was reported in up to 30percent of patients with rectal cancer (11,12). Following refinement of surgical technique (6), globally, local recurrence rates for rectal cancer were reduced to less than 10 percent and is now the standard of care (13). The use of preoperative chemoradiation to induce size reduction and tumour margin regression, and therefore, a cancer-free margin of resection of the rectum was established in a randomized controlled trial in 2004 (14). Pre-operative chemoradiation for locally advanced cancer of the lower rectum (stage T2 with nodal involvement, stage T3 and T4), is now the standard of care for patients with rectal cancer.

It was found that the use of pre-operative chemoradiation for rectal cancer resulted in regression of tumour either in part or whole. We reported rectal cancer regression following long-course chemoradiation in up to 58 percent of our patients with rectal cancer (15). The observation of a complete response of rectal cancer to treatment by preoperative chemoradiation was first proposed by a group in Brazil, in 1998 (16). These authors proposed that, in a small proportion of patients with rectal cancer who received pre-operative chemoradiation (c-RT), it seemed safe to adopt a non-operative "watch-and-wait" approach with close and frequent observation for recurrent cancer, which was subsequently treated by operative resection. Their conclusion was based on a longitudinal study of rectal cancer patients who displayed a pathologically complete response (p-CR) following pre-operative c-RT for over two decades, which showed that there was no difference in overall survival between those who had had a pathologically complete response and no surgical intervention versus those who underwent surgical resection following a complete pathological tumour response (16).

This study, supported by a systematic review of 867 patients (17), forms the basis for the current globally accepted "watch-and-wait" policy for treatment of selected patients with rectal cancer, especially in those of advanced age, the risk of mortality from co-existing disease, and in those who preferred not to undergo surgery following pre-operative counselling. We now know that up to 25% of patients with rectal cancer treated with long-course pre-operative chemoradiation (18) will achieve a pathologically complete response - defined as the absence of viable tumour cells in the removed surgical specimen after neoadjuvant treatment (19), and a surgical-radiological consensus that a near-complete response is a temporary responsa 6-month period of observation followed by evolution of a complete response after a longer waiting interval (20).

Synopsis

The incidence of colorectal cancer has increased in Sri Lanka over the years. Up to 60 percent of patients will have cancer of the rectum. The current standard treatment of rectal cancer includes long-course chemoradiation for 5weeks (5040cGy over 25 fractions) followed by a waiting period of 10 to 12 weeks, repeat assessment of tumour response (clinical assessment that includes digital rectal exam, endoscopy and magnetic resonance imaging) a week before consideration for the optimum choice of surgical resection, that is, anal sphincter-saving resection of the rectum and restoration of intestinal continuity versus abdomino-perineal resection of the anorectum with a permanent colostomy. In a minority the "watch-and-wait" non-operative policy is adopted.

Chemotherapy for Rectal Cancer

Since 2004, chemotherapy had been used to treat mid- and low rectal cancer in the pre-operative (neoadjuvant) setting as part of long-course neoadjuvant chemoradiation (14) for T2 tumours with lymph node involvement, T3 rectal cancer that involved the entire thickness of the rectum and its surrounding envelope of fat (mesorectum), and T4 tumours. Currently, the most reliable assessment of wall invasion in rectal cancer, that is, T-stage assessment, is by magnetic resonance imaging, with an accuracy of 92% (21). The main role of chemotherapy, which is used in the first and last weeks of the 5-week pre-operative chemoradiation schedule, is to serve as a sensitizing agent for radiotherapy (22).

5-Fluorouracil (5-FU) is the most frequently used chemotherapeutic agent in treatment of rectal cancer. The active component is a fluorinated pyrimidine that interrupts the synthesis of DNA by blocking thymidilic acid formation (23). Known side-effects are diarrhoea that will require dose adjustment, and peripheral neuropathy. Although 5-fluorouracil remains the mainstay of chemotherapy for rectal cancer, in recent years, use of combination chemotherapy regimens has expanded because of the incomplete efficiency of chemotherapy and its substantial side effects. For example, Margalit et al showed that elderly patients had difficulty coping with combined chemotherapy and required interruptions of treatment and, at times, early termination of treatment (24). Combination therapy proved more effective and is typically based on 5-fluorouracil, or its prodrug capecitabine, in combination with levamisole and leucovorin (25).

Adjuvant chemoradiation therapy Based on guidelines, patients with locally advanced mid and low rectal cancer, up to 10cm from the anal verge, (T3-4, N0, M0 or any T, N1-2, M0) should receive upfront chemotherapy and radiotherapy before surgical resection. The combination of preoperative radiation therapy and chemotherapy with fluorouracil improves local control, distant spread, and survival (16,17,18). The basis of this improvement is believed to be the activity of fluorouracil as a radiosensitizer. Surgical resection can be undertaken up to 10 weeks after completion of chemotherapy and radiotherapy.

A meta-analysis of neoadjuvant long-course chemoradiotherapy followed by total mesorectal excision for locally advanced rectal cancer concluded that waiting for a minimum of 8 weeks from the end of chemoradiotherapy to surgical excision increased pathological complete response, downstaging rates, and improved recurrence-free survival without compromising surgical morbidity. With longer intervals, the odds ratio (OR) for p CR was 1.41 (95% confidence interval \[CI\] 1.30-1.52; P \< 0.001) and the OR for tumour downstaging was 1.18 (95% CI 1.05-1.32; P = 0.004). The increased rate of p CR translated to reduced rates of distant metastasis and overall recurrence but not local recurrence (26). This means that the risk of local recurrence of rectal cancer after a pathological complete response remained at 20% compared with less than 10% if a patient with a complete response underwent surgical resection of the irradiated rectum. (27).

Synopsis- Chemotherapy for Rectal Cancer Traditionally, 5-fluorouracil based chemotherapy was used to treat node positive rectal cancer, that is, following surgical resection and histopathological assessment, and stage 4 metastatic rectal cancer. Since 2004, chemotherapy was used in a neo-adjuvant setting to help sensitize rectal cancer during long-course irradiation treatment and to achieve reduction in size and stage of rectal cancer. Latterly, total neo-adjuvant therapy has shown signs of a greater number of rectal cancers achieving a complete response compared with rectal cancer treated by standard pre-operative chemo-RT. The term TNT refers to a number of new multi-modal treatments for locally advanced rectal cancer that administer preoperative irradiation and systemic chemotherapy before surgical resection. Currently, these strategies can vary substantially in their doses of irradiation, fractionations, chemotherapy options and sequencing, and remain non-standardised. However, what is common amongst all regimes of TNT is that they offer irradiation and "full" chemotherapy as opposed to sensitizing doses of chemotherapy as is used in the standard neo-adjuvant therapy (28). The underlying principle of TNT is to provide systemic per-operative chemotherapy rather than a sensitizing dose as in standard neo-adjuvant chemoradiation. The current perceived advantages of TNT are that a greater number of patients will complete their chemotherapy and that there is greater likelihood of achieving a pathologically complete response in rectal cancer compared with standard neoadjuvant therapy (29) - this approach seemed to reduce local recurrence for rectal cancer from around 35% to 5%-10% and, more importantly, significantly improved overall survival. Thus, local recurrence now seems of low-level concern compared with distant metastasis that is now the leading cause of rectal cancer-related death.

Rationale for Ayurvedic treatment use:

Successful treatment of rectal cancer comprises of several stages including diagnosis, accurate staging, neoadjuvant treatment (if indicated) to improve operability and reduce the risk of local recurrence. However, most cancer related deaths are linked to metastatic spread of the cancer (29, 30). Patients with metastatic disease carry a poor prognosis and, in such patients, metastatic disease accounts for 90% of cancer related deaths (31) The remaining 10% will arise from complications of surgery and other forms of treatment. Therefore, cancer metastasis as a target for therapy cannot be ignored. To treat cancers successfully we must inhibit metastatic processes and develop strategies that do not rely on primary tumour responses (30). The development of new effective medicines that interrupt the primary causes of metastasis is an important challenge. Mechanistically, metastatic tumour cells are genetically unstable, and in most cancers no single dominant pathway is likely to control metastasis (32,33). Also, the extent to which tumour cells have left the primary tumour and established micrometastasis before cancer diagnosis is generally acknowledged but poorly understood (34). It is plausible that surgery itself may have a contributory role in future development of metastatic disease. To alter events at the time of surgery and thus reduce the risk of future metastatic disease, peritumoural injections of local anaesthetic have been tried in patients with breast cancer. Local anesthesia blocks voltage-gated sodium channels and prevents activation of prometastatic pathways. This resulted in improvements in disease