Preoperative CRT With Temozolomide Plus Capecitabine in Rectal Cancer

• Maximum tolerated dose (MTD) [ Time Frame: 5-6 weeks during study treatment ] [ Designated as safety issue: Yes ]
  The MTD is defined as the maximum dose level in the doses of temozolomide tested with capecitabine and radiation in which the incidence proportion of DLT exceeds 30%.
  
  
• Recommended dose (RD) [ Time Frame: 5-6 weeks after CRT ] [ Designated as safety issue: No ]
  RD will be defined as one level below the MTD.
  
  

• Association between MGMT expression and pathologic responses [ Time Frame: at the time of surgery (6-8 weeks after study treatment) ] [ Designated as safety issue: No ]
  

• Toxicity [ Time Frame: 5-6 weeks during study treatment ] [ Designated as safety issue: Yes ]

  Toxicity will be monitored and recorded every week during study treatment (5 or 6 weeks) as following according to the NCI-CTCAE version 4.0

  1. An interval history and physical examination with particular attention to drug-induced side effects along with documentation of the patient's weight and performance status will be performed on each visit.
  2. CBC with differential count, blood chemistry including calcium, phosphorus, glucose, BUN, creatinine, total protein, albumin, AST, ALT, alkaline phosphatase, total bilirubin, and electrolyte will be performed before next planned treatment.
  3. All relevant information regarding drug dosage, laboratory examinations, and treatment-related toxicities must be recorded before each treatment is given.
  4. Summaries of the frequency and severity of adverse effects are based on the worst episodes recorded.
  
  
• Efficacy [ Time Frame: after surgery (6-8 weeks after study treatment) ] [ Designated as safety issue: No ]

  Efficacy: Pathologic major responses = total regression + near total regression.

  We will carefully inspect the circumferential resection margin, defining a positive margin as any residual tumor within ≤ 1 mm of the circumferential margin.

  Pathologic responses and stages will be classified according to Dworak's classification1 and the AJCC (American Joint Committee on Cancer) staging system, respectively. In each case, the entire tumor including mesorectal fat will be serially sliced into 4-mm-thick sections and embedded in paraffin.

  A pathologic complete response is defined as grade 4 tumor regression; with residual fibrotic mass or acellular mucin pools only, thus without detectable tumor cells

  A near total response is defined as grade 3 tumor regression; with very few tumor cells in fibrotic tissue with or without mucous substance.

  
  
• Disease-free survival [ Time Frame: 3-year or 5-year after surgery ] [ Designated as safety issue: No ]
  

Preoperative chemoradiation (CRT) with fluoropyrimidine (5-fluorouracil or capecitabine) is now regarded as a standard treatment option in patients with locally advanced resectable rectal cancer, and pathologic response rates and tumor regression grades after preoperative CRT have been proved to be important prognostic factors for survival outcomes. Several studies of preoperative CRT with fluoropyrimidines plus other agents, such as oxaliplatin, irinotecan, cetuximab, and bevacizumab, have been performed to improve pathologic response rates; however, they have failed to show improved results compared to those with fluoropyrimidine alone. Thus, fluoropyrimidine alone is a standard chemotherapeutic strategy in patients with locally advanced resectable rectal cancer who will be treated with preoperative CRT at present; further studies are needed to find effective combination for improving pathologic responses other than fluoropyrimidines alone in these patient population.

Temozolomide is an oral alkylating agent, and has been proved to be effective in patients with glioblastoma or high grade anaplastic glioma when administered with concurrent radiotherapy either as adjuvant or recurrent settings, and also seemed to be effective in patients with malignant melanoma either as monotherapy or combination chemotherapy. Temozolomide has been known to deplete O6-methylguanine DNA methyltransferase (MGMT), which is one of the DNA repair enzymes, and recent studies have shown that lower expression (by immunohistochemistry) or hypermethylation (by methylation-specific PCR) of MGMT could be a predictive marker of better responses to treatment with temozolomide in patient with glioblastoma, high grade anaplastic glioma or malignant melanoma.

Silencing of MGMT by promoter hypermethylation has been known to involve colorectal carcinogenesis pathway by the association with KRAS mutation and low-CIMP (CpG island methylation phenotype), and hypermethylation of MGMT promoter could be detected in 29% to 46% of tumor tissues from sporadic colorectal cancer patients. Nagasaka et al. showed notable results that MGMT promoter methylation status was associated with microsatellite instability and hypermethylation of MGMT promoter could be a predictive factor of low recurrence in colorectal cancer patients with adjuvant oral fluoropyrimidine chemotherapy after curative surgery. In addition, Shacham-Shmueli et al. showed that temozolomide could be an additional treatment option in a small group of patients with chemotherapy-refractory metastatic colorectal cancer which had lower MGMT expressions.