KRAS Information

1. Who are candidates for K-ras Mutation Detection?

If the candidate meets the following criteria, K-ras Mutation Detection test could be available:

Patient has been diagnosed with metastatic colorectal cancer.
Patient has failed on fluoropyrimidine-, oxaliplatin-, and irinotecan-containing chemotherapy regimens.
Patient will be prescribed Vectibix™ or Erbitux® if the results of the K-ras test indicate the tumor is non-mutated (wild-type) K-ras.

For Health Care Practitioners who require more information on Vectibix®, please visit Amgen Canada’s Vectibix.ca website.

Other indications when K-ras Mutation Detection would be helpful include:

Patients currently treated with Vectibix™ (panitumumab) or Erbitux® (cetuximab) for colorectal cancer (or prior to commencing treatment).
Patients with lung cancer under treatment with tyrosine kinase inhibitors such as Iressa™ (AstraZeneca) or Tarceva™ (Roche/OSI Pharmaceuticals).

Please visit the Colorectal Cancer Coalition website for more information.

2. K-ras Mutation Detection - Background Information

a) Colon Cancer:
Virtually 98% of all cancers in the large intestine are adenocarcinomas, with a peak incidence between ages 60 and 79. Less than 20% of cases occur in patients less than 50 years old. There is no gender difference in the incidence of colon cancer.

Environmental factors, particularly dietary practices, are implicated in colon cancer and are believed to be effected by geographic location (higher death rates in US, Australia, New Zealand, and Eastern European countries, and substantially lower death rates in Mexico, South America and Africa). Obesity and physical inactivity are also considered as risk factors for colon cancer.

Epidemiological studies showed that use of aspirin and other NSAIDs has protective effect against colon cancer. Lymph nodes, liver, lungs and bones are considered favoured sites of metastatic spread, followed by many other sites. In 25% to 30% of patients, the disease has spread beyond the range of curative surgery.

The extent of the tumor (tumor stage) at the time of diagnosis is the single most important prognostic indicator of colorectal carcinoma. Currently, most countries use the tumor-nodes-metastasis (TNM) classification and staging system from the American Joint Commission on cancer.

TNM classification of Carcinoma of the Colon and Rectum (used for both clinical and pathologic staging)
Primary Tumor (T)
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
Tis	Carcinoma in situ: intraepithelial or invasion of lamina Propria
T1	Tumor invades submucosa
T2	Tumor invades muscularis propria
T3	Tumor invades through the muscularis propria into the suberosa, or into non-peritonealized periocolic or perirectal tissues
T4	Tumor directly invades other organs or structures, and/or perforates visceral peritoneum
Regional Lymph Nodes (N)
Nx	Regional lymph nodes cannot be assessed
N0	No regional lymph node metastasis
N1	Metastasis in 1 to 3 lymph nodes
N2	Metastasis in 4 or more lymph nodes
Distant Metastasis (M)
Mx	Distant metastasis cannot be assessed
M0	No distant metastasis
M1	Distant metastasis

STAGE GROUPING
Stage	T	N	M	Dukes	MAC
0	Tis	N0	M0	-	-
I	T1	N0	M0	A	A
	T2	N0	M0	A	B1
IIA	T3	N0	M0	B	B2
IIB	T4	N0	M0	B	B3
IIIA	T1-T2	N1	M0	C	C1
IIIB	T3-T4	N1	M0	C	C2/C3
IIIC	Any T	N2	M0	C	C1/C2/C3
IV	Any T	Any N	M1	-	D

American Joint Committee on Cancer, 2002, Cancer Staging Manual, Sixth Edition, page 115-116

b) K-ras Mutation Detection in Treatment of Colorectal Cancer:

Colon cancer is the third most frequently detected cancer worldwide, accounting for close to 1 million new patients every year. Colon cancer has the third highest mortality rate, following lung and breast cancer. Seventy to eighty percent of patients have a potentially curative disease; however close to 50% of patients will develop metastases (liver being the most common site).

Resistance to conventional chemotherapy is likely the main reason for disease progression. Less than 10% of patients with disseminated disease will survive for five or more years (1).

Recent publications on colorectal cancer have shown the benefit of using the epidermal growth factor receptor (EGFR) in treatment strategy. EGFR is a trans-membrane glycoprotein and one of the four HER-family tyrosine kinases (EGFR, erbB2, erbB3, erbB4) which initiate intracellular proliferation signaling (2). Epidermal growth factor (EGF), transforming growth factor alpha (TGF-), amphiregulin and betacellulin are the main ligands for EGFR (3).

The activation of EGFR results in cell proliferation and survival through the Ras/Raf/MEK/ERK or PI3K/PTEN/AKT pathways, respectively (1). Activated EGFR also regulates the production of angiogenic factors and permits tumor invasion through extra-cellular matrix components. About 70% of cases with metastatic colorectal cancer have EGFR expression. This correlates with poor prognosis (4). Therefore, these studies open the new approaches to inhibit EGFR through monoclonal antibodies and small molecular inhibitors.

Anti-EGFR targeted antibodies such as cetuximab and panitumumab, administered as monotherapy in colorectal cancer, show response and disease stabilization rates of approximately 10% and 30%, respectively (5;6). However, clinical experience shows that level of EGFR expression as measured by immunohistochemistry does not predict clinical benefits (2;5;7)

K-ras, the human homolog of the Kirsten rat sarcoma-2 virus oncogene, encodes a small GTP-binding protein that acts as a self-inactivating signal transducer by cycling from GDP- to GTP-bound states in response to stimulation of a cell surface receptor, including EGFR (8;9)

The incidence of K-ras mutations is about 30 to 35 % in colon cancer patients. Recent studies showed an inverse correlation between K-ras mutations and response to anti-EGFR therapy (3). Amado RG (10)presented the higher sample-size data which showed that patients with K-ras mutations had 70% progressive disease where wild-type K-ras patients showed 36% progressive disease. For K-ras mutated patients in this study, panitumumab offered no benefit. In a similar smaller-sized study on Cetuximab (11) none of 42 K-ras mutated patients obtained treatment benefit, where as 27 out of 66 wild-type K-ras patients responded to therapy.

Overall, current studies for the first time provided evidence on the critical role of K-ras Mutation Detection in advanced colon cancer as a predictor of evaluation and response to EGFR agents.

c) K-ras Mutation Detection Assay:
During the last few years, clinical trials on colorectal cancer patients made discoveries related to personal genetic differences which could affect treatment regimens. Current studies showed that monoclonal antibodies against EGFR are not beneficial in patients with mutations in K-ras oncogenes. The most significant results indicated that successful treatment of metastatic colorectal cancer could be directly linked to the activation of K-ras signaling pathways.

Currently, there are different methods available to detect the K-ras mutations, from sequencing, mini-sequencing, using one-step polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) analysis, to commercially available kits based on allele-specific PCR (ARMS) and Scorpions® real-time PCR technology. MOUNT SINAI SERVICES (MSS) is currently using the K-ras Mutation Detection Kit based on ARMS and Scorpions® real-time PCR technology (www.dxsdiagnostics.com).

d) Links:
There are many web sites issued by governments or societies which provide detailed information on colorectal cancer. The following list provides just few of these web sites:

The Susan Cohan Kasdas Colon Cancer Foundation

Colon Cancer Check

Canadian Cancer Society

Colorectal Cancer Screening Initiative Foundation

References:

1. O'Connell JB, Maggard MA, Ko CY. Colon cancer survival rates with the new American Joint Committee on Cancer sixth edition staging. J Natl Cancer Inst 2004;96:1420-5.

2. Adams R, Maughan T. Predicting response to epidermal growth factor receptor-targeted therapy in colorectal cancer. Expert Rev Anticancer Ther 2007;7:503-18.

3. Lievre A, Bachet JB, Le CD, Boige V, Landi B, Emile JF et al. KRAS mutation status is predictive of response to cetuximab therapy in colorectal cancer. Cancer Res 2006;66:3992-5.

4. Mayer A, Takimoto M, Fritz E, Schellander G, Kofler K, Ludwig H. The prognostic significance of proliferating cell nuclear antigen, epidermal growth factor receptor, and mdr gene expression in colorectal cancer. Cancer 1993;71:2454-60.

5. Cunningham D, Humblet Y, Siena S, Khayat D, Bleiberg H, Santoro A et al. Cetuximab monotherapy and cetuximab plus irinotecan in irinotecan-refractory metastatic colorectal cancer. N Engl J Med 2004;351:337-45.

6. Van CE, Peeters M, Siena S, Humblet Y, Hendlisz A, Neyns B et al. Open-label phase III trial of panitumumab plus best supportive care compared with best supportive care alone in patients with chemotherapy-refractory metastatic colorectal cancer. J Clin Oncol 2007;25:1658-64.

7. Chung KY, Shia J, Kemeny NE, Shah M, Schwartz GK, Tse A et al. Cetuximab shows activity in colorectal cancer patients with tumors that do not express the epidermal growth factor receptor by immunohistochemistry. J Clin Oncol 2005;23:1803-10.

8. Downward J. Targeting RAS signalling pathways in cancer therapy. Nat Rev Cancer 2003;3:11-22.

9. Schubbert S, Shannon K, Bollag G. Hyperactive Ras in developmental disorders and cancer. Nat Rev Cancer 2007;7:295-308.

10. Amado RG, Wolf M, Peeters M, Van CE, Siena S, Freeman DJ et al. Wild-type KRAS is required for panitumumab efficacy in patients with metastatic colorectal cancer. J Clin Oncol 2008;26:1626-34.

11. De RW, Piessevaux H, De SJ, Janssens M, De HG, Personeni N et al. KRAS wild-type state predicts survival and is associated to early radiological response in metastatic colorectal cancer treated with cetuximab. Ann Oncol 2008;19:508-15.