Japan tackles rising deaths from gastrointestinal cancer

The number of deaths caused by gastrointestinal cancers is on the rise in Japan, due in part to a shift toward Western-style eating habits. Early detection of these cancers is one way to address this trend. Advances in medical imaging technologies will enable radiologists to play a key role in this effort, according to speakers at the 2005 European Congress of Radiology in March.

Mortality associated with colorectal cancer is increasing annually, Prof. Yutaka Imai said during a special session showcasing Japanese expertise in the imaging-pathologic correlation of early gastrointestinal cancer. Deaths from gastric cancer have begun to fall slightly, indicating the value of prompt diagnosis and treatment, but the incidence of this malignancy remains high in Japan.

Japanese cancer associations classify early gastric and colorectal cancers as "type 0," which is subdivided into subtype I (elemental), IIa (superficial elemental), IIb (superficial flat), IIc (superficial depressed), or III (depressed).

"Detection of the superficial type of early gastric and colorectal cancers is very important for the reduction of these cancers in Japan," said Imai, a professor of radiology at Tokai University School of Medicine in Kanagawa.

Double-contrast radiography (DCR) and optical endoscopy are the primary tools for cancer detection in the gastrointestinal tract. Imai showed a selection of cases illustrating typical imaging findings for superficial IIb and IIc gastric cancers. Completely flat superficial tumors, which are difficult to see on endoscopy, can be detected by characteristic irregular mucosal patterns on DCR (Figure 1). Recognition of superficial depressed lesions on radiography is important because this is the most common form of early gastric cancer.

Multislice CT could potentially provide another tool for diagnosing and staging early-stage colorectal and gastric cancers. Imai described a case in which both MSCT gastrography and optical endoscopy revealed a slightly elevated flat lesion (IIa) in the same location. Histological analysis following mucosal resection confirmed a well-differentiated adenocarcinoma with invasion limited to the mucosa.

Endoluminal MRI helps in preoperative tumor staging of rectal cancers, Imai said. Research suggests that T2-weighted images of rectal cancer performed with an endorectal surface coil provide the best way to evaluate local tumor invasion (Figure 2).

"Use of an endorectal surface coil can define intramural tumor infiltration by depicting all layers of the internal wall," he said.

Early detection of pancreatic cancer is especially critical because the malignancy is one of the most difficult to treat, said Prof. Hiromu Mori, a professor of radiology at Oita University, Japan.

"The prognosis of patients with pancreatic cancer is very poor. Few patients with stage I pancreatic cancers are found because there is no established screening method," he said. "Furthermore, even T1 cancers infiltrate to the surrounding pancreatic tissues."

Pancreatic cancers are defined as early-stage if they are margin-negative following resection. This criterion excludes tumors with invasion to extrapancreatic nerve plexuses, to roots of peripancreatic mesenteries, and to the superior mesenteric-portal venous axis.

MSCT examinations, combined with anatomic knowledge of the extrapancreatic nerve plexuses, pancreatic veins, and lymphatic pathways, can be used to assess the tumors' invasiveness. Identification of local invasion and metastasis formation helps determine whether surgical intervention is worthwhile. Imaging can also help differentiate masslike chronic pancreatitis and focal autoimmune pancreatitis from carcinoma, again potentially preventing unnecessary surgery, Mori said.

Research is under way to develop an effective screening method for early-stage pancreatic cancer. One suggestion is periodic ultrasound checkups to detect dilations to the main pancreatic duct or cyst like findings. Careful follow-up of patients with intraductal papillary mucinous neoplasms (IPMN) of the pancreas would be a valuable strategy to adopt, Mori said. IPMN frequently develops into cancer, but patients with IPMN and invasive cancer in the adjacent pancreatic parenchyma generally have a much better chance of survival than patients with the usual ductal pancreatic carcinoma.

Biliary tract cancers are seldom detected at an early stage, said Dr. Shinji Hirohashi, an associate professor of radiology at Nara Medical University, Japan. Patients generally do not experience symptoms until the malignancy is reasonably advanced.

"Early gallbladder cancer is often discovered only when the gallbladder cancer is removed as treatment for ulcers. And other biliary tract cancers are often very advanced by the time they are diagnosed," Hirohashi said.

The prognosis for patients with advanced biliary tract cancer is poor, but when the cancer is caught early, complete resection can prove extremely effective. Endoscopic ultrasound and intraductal ultrasound, which show the layering structure of the gallbladder and bile duct wall, offer an effective means of diagnosing and staging the disease. Abdominal ultrasound should therefore be added to routine medical checkups as a screening tool for biliary tract cancer, Hirohashi said.