Colon cancer

Anatomy
Intraperitoneal segments of colon: transverse and sigmoid colon
Retroperitoneal: Ascending, descending colon; rectum (distal 1/3 of rectum has no peritoneal covering at all)
Rectum extends from peritoneal reflection of sigmoid to the anorectal ring (12 - 15cm long)
Nodal drainage: pericolic/mesenteric nodes for colon; perirectal, presacral, internal iliac (rectal)

Epidemiology
3rd most common cancer in US
~150,000 cases per year, 50,000 deaths

Risk factors
Age
Male sex
Family history
Obesity
High intake of processed meats
EtOH

Hereditary syndromes associated with colorectal cancer
Lynch syndrome
HNPCC
Familial adenomatous polyposis
Li-Fraumeni syndrome

Pathology
Vast majority of tumors are adenocarcinoma
Polyps increase the risk of colon cancer from 6% to 15% (lifetime)
Villous adenomas (villains) are at the highest risk of transforming into malignancies
Molecular biology: mutated APC, p53, ras, HNPCC (correlated with microsatellite instability)

Staging workup
Colonoscopy
EUS (rectal tumors only)
Bloodwork: CBC, LFT, CEA
CT chest/abdomen/pelvis or PET CT

Prognostic factors
Depth of invasion
Nodal stage

Colon cancer treatment
Role of xrt is limited
Primary therapy is surgical (hemicolectomy)
Adjuvant chemo indicated in stage III patients (any node+ or T3-4 disease)
Standard regimen is 5FU/leucovorin, oxaliplatin ("FOLFOX")
In tumors with adherence/invasion of adjacent structures (more common in ascending and descending colon where clearing radial margins is more difficult), adjuvant xrt may be indicated

Adjuvant RT for colon cancer
Intergroup 0130 (PMID 15249584)
Patients with completely resected colon cancer that was either adherent to adjacent structures, penetrated the serosa, or was node +, were assigned to chemo alone vs. chemoRT (50.4Gy to tumor bed and draining nodes)
5 year DFS (~50%) and OS (~60%) were not statistically different in the two arms
The study had to be closed early due to poor accrual
No benefit was seen in any subset of patients

Massachusetts General retrospective experience (PMID 10439171)
Benefit to adjuvant RT (for DFS and local control) was observed in patients who had:
-Tumor associated abscess or fistula
-Residual disease
-Serosal penetration
-Node + disease
Note that only about 30% of patients received chemo with radiation

Current indications for RT (usually given with concurrent 5FU)
1) tumor associated abscess/fistula
2) invasion of adjacent structures
3) positive margins
4) ability to identify a non-mobile target