Lesions of the Lower Intestinal Tract
Moderators: Dr. Henry Appelman and Dr. Joel K. Greenson
Case 11 -
Depressed type submucosal carcinoma
66-year-old female, was symptom-free and requested a colonoscopic examination for cancer screening.
Depressed type lesion was found in the rectum. Biopsy and subsequent surgical operation was done.
The rectal lesion measuring 15 mm in diameter is a depressed type epithelial neoplasm with minute
invasion to the submucosa. Low-power scans of the lesion indicate that the depression is formed by a
reduction in the thickness of the neoplastic mucosa, which is thinner than the surrounding normal mucosa.
The histological feature of the lesion is rather uniform. Architecturally, it consists of simple
straight tubules with little branching, but shows high-grade cytology evidenced by nuclear enlargement,
condensed or vesicular nuclear chromatin and prominent nucleoli. In one of two sections, few dilated
neoplastic glands separate the muscularis mucosae and invade into the submucosa at the center of the
lesion. In other section, there is a probable biopsy scar which is characterized by disappearance of the
muscularis mucosae and fibrosis in the submucosa.
Case 11 - Slide 1
The depressed type tumor is a recently recognized morphological type of colorectal epithelial
neoplasm. It can be a pure depression or can be accompanied by a slight marginal elevation composed
either neoplastic mucosa or reactive hyperplastic mucosa.  It has been reported by Japanese
workers alone since 1980's,
but now the lesion is described throughout the world.
 It comprises adenoma, intramucosal carcinoma (by Japanese histological criteria which is
equivalent to adenoma with severe dysplasia according to WHO system ) and submucosal invasive
carcinoma. When we confine the discussion to "submucosal carcinoma", depressed type comprised 6%
(25/302) of them in our series of surgically resected materials,  and 0 to 3.1% of all
neoplastic lesions found in endoscopic examinations.
Average size of the tumor in our
series was 14.5 mm in diameter, which was significantly smaller than that of polypoid type submucosal
carcinoma (24.6mm). 
The depressed type tumor shows the high rate of submucosal invasion by small size compared to
the polypoid type. In a large-scaled study of Kashida et al. which examined 22,402 colorectal
neosplasms resected endoscopically or surgically, the invasive rates of depressed type were 7.9%
in lesions not exceeding 5mm, 44.9% in those of 6-10mm, and 69.9% in those of 11-15mm,
while those of polypoid type were 0%, 1.3% and 7.7%, respectively.  This strongly
suggests that the depressed type tumor grows rapidly at an early stage to become advanced cancer, and
implies that the true incidence of depressed type submucosal carcinoma in general population
would be higher than ones described above.
The recognition that colorectal cancer can appear as depressed type has an important clinical
implication. The polyp-cancer sequence  has led endoscopists to focus on polypoid
lesions when screening for tumors. However, it is stressed that ones have to pay attention to
non-polypoid depressed type tumors, as well, in order to detect early stage of colorectal carcinoma.
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