Lesions of the Lower Intestinal Tract
Moderators: Dr. Henry Appelman and Dr. Joel K. Greenson
Case 1 -
Poorly differentiated colon adenocarcinoma in a patient with Hereditary
Nonpolyposis Colorectal Carcinoma
A 58 year old man was found at routine colonoscopy to have 2 colon tumors, one in his transverse
colon and the other in his rectosigmoid. He was healthy and had no previous medical illnesses. His
family history was significant for multiple family members with tumors including colon and endometrial
carcinoma, ureter and kidney tumors, skin tumors, and thyroid and brain tumors. The family history met
the Amsterdam criteria for the diagnosis of Hereditary Nonpolyposis Colorectal Cancer (HNPCC). Biopsies
were performed followed by colectomy.
The colectomy specimen contained 2 tumors measuring up to 9 cm at maximum dimension. Microscopic
sections through the rectosigmoid tumor showed an adenocarcinoma with a pushing border that extended into
the muscularis propria. There was a surrounding Crohn's-like reaction. The growth pattern of the tumor
varied from a diffuse proliferation to sheets to nests of malignant cells with poorly differentiated
glands in some areas. Many areas contained intraepithelial lymphocytes. All 28 lymph nodes were
negative for metastasis. The rectosigmoid tumor was a T2 carcinoma while the transverse tumor was a T3
carcinoma. Immunohistochemical stains for the mismatch repair proteins were evaluated and MLH1 and PMS2
were present, whereas, MSH2 and MSH6 were absent. The tumor was found to be microsatellite unstable by
PCR analysis of tumor DNA and gene sequencing revealed a mutation in MSH2 (942+3a>t) confirming a
diagnosis of Lynch syndrome. Family screening revealed the same mutation in 2 of 4 sisters, 2 of 5
brothers, 1 of 2 daughters, 1 of 2 nieces, 1 of 1 nephew, and 1 of 1 grand niece. Clinically, this
family can be considered to have both the Muir-Torre variant due to the history of skin tumors in the
family (sebaceous adenoma) and the Turcot variant due to the family history of brain tumor (brother with
Case 1 - Slide 1
Hereditary Non-Polyposis Colorectal Carcinoma (HNPCC) is the most common hereditary
colorectal carcinoma syndrome and accounts for 2 to 4% of colorectal carcinoma in the United States.
Patients with HNPCC are at high risk for developing colorectal and many extracolonic tumors including
endometrial carcinoma. The age at onset is early but variable. HNPCC is caused by mutations in the
mismatch repair genes.
Microsatellite instability (MSI) occurs when tissues acquire numerical nucleotide variability in
repetitive DNA sequences due to abnormalities in the mismatch repair proteins. MSI is detected in 50-80%
of tumors from patients with HNPCC, and is present in 15-20% of unselected colorectal cancer cases, some
of which may be due to Lynch Syndrome.
Lynch Syndrome is defined as carcinoma having MSI due to a germline mutation in one of the DNA
mismatch repair genes, MLH1, MSH2, MSH6 or PMS2. In sporadic colorectal cancer, MSI is
related to epigenetic silencing of the MLH1 gene by hypermethylation of the
promoter region. The inability to repair somatic gene mutations raises the possibility that mutations
will accumulate within a cell. These accumulated mutations are the underlying basis for cancer
Because the majority of HNPCC associated colorectal tumors also represent Lynch Syndrome and have an
analyzable gene defect, testing for MSI is an important screening/diagnostic tool. MSI testing
identifies patients and families who need a detailed study of germline DNA to confirm germline mutation
in order to make the diagnosis of Lynch syndrome. The detection of MSI in sporadic colorectal carcinomas
has prognostic value in that cancers with a high level of microsatellite instability have an improved
overall survival and may have a different response to adjuvant therapy.
The National Cancer Institute Workshop on HNPCC Syndrome defined a set of criteria that when met
warrant MSI tumor testing. These criteria are known as the Bethesda guidelines. There is evidence that
the Bethesda criteria are more sensitive (and less specific) than either the Amsterdam I or II criteria
in identifying potential Lynch Syndrome patients and families with pathogenic mutations. Included in the Bethesda criteria are certain histopathologic criteria that help
identify MSI colorectal carcinoma, specifically, poorly differentiated or undifferentiated tumors and
signet ring cell type colorectal carcinoma.
Certain histologic features of microsatellite unstable tumors have been described, including well
circumscribed tumors with pushing borders and a prominent host lymphocytic infiltrate. The host reaction
can include intraepithelial lymphocytes, peritumoral lymphocytes and/or a Crohn's-like reaction. Some
tumors are poorly differentiated with epithelium disposed in small clusters and irregular trabeculae or
large aggregates with intraepithelial lymphocytes. This subtype has been described as medullary or
undifferentiated, though the majority contains sub-clones in which glandular differentiation is
evident. Among the histologic features,
mucinous histology and intraepithelial lymphocytosis correlate the most with MSI. Several studies
have tried to identify features that can differentiate tumors from patients with Lynch Syndrome from
those with sporadic MLH1 promoter methylation. Many authors agree that
although Lynch syndrome tumors are more often poorly differentiated, mucin producing, or of the signet
ring cell and medullary type, there is no specific histologic type that can differentiate patients with
Lynch Syndrome from those with sporadic MLH1 promoter methylation.
Columbus area HNPCC study
The Columbus Ohio area HNPCC study evaluated all patients with newly diagnosed colorectal carcinoma. In the initial
1066 patients, 19.5% were found to have microsatellite instability (MSI high and low) and 2.2% (23
patients) were found to have HNPCC. Of these 23 patients, 10 were greater than 50 years old and 5 did
not meet clinical Amsterdam or Bethesda criteria. The families of 21 HNPCC patients were screened and an
additional 52 cases of HNPCC were identified. Therefore, routine screening for HNPCC is useful in
unselected colorectal carcinoma patients. Screening using immunohistochemistry was found to be at least
as useful as screening by MSI genotyping.
In order to detect Lynch syndrome, the family and personal history are vital. Amsterdam Criteria
standardize the clinical criteria for diagnosis, while Bethesda Guidelines help identify patients for MSI
testing. Both together are less than 50% sensitive in unselected patients. Typical histologic features
in microsatellite unstable colorectal carcinomas include intraepithelial lymphocytes, mucinous carcinoma,
signet ring cells, medullary carcinomas and tumor heterogeneity. The sensitivity is fairly low (up to 40
%) but the specificity is better (up to 95% with some features). Immunohistochemistry for the mismatch
repair proteins can be helpful to direct genetic testing. All proteins are normally present in the
colonic epithelial cells. If a protein is absent, the associated protein is not being expressed
(mutation or methylation). If any protein is absent, the tumor can be assumed to be microsatellite
unstable. MSI analysis can be performed on tumor DNA to detect microsatellite instability.
Whether MSI analysis and/or immunohistochemistry are performed initially depends on the center. MSI
and immunohistochemistry both have pitfalls. MSI analysis requires a molecular laboratory and normal
tissue or blood for comparison while immunohistochemistry does not. Pitfalls in MSI analysis include
intratumoral heterogeneity and problems with tumors containing a low percentage of malignant cells
including mucinous tumors. Problems with immunhistochemistry include the need for expertise to stain and
interpret slides, intratumoral variability in staining, and the interpretation of cytoplasmic staining.
Immunohistochemistry has the advantage of being readily available in any pathology laboratory and normal
tissue is not needed. Additionally, Immunohistochemistry may be used to direct molecular testing since
it predicts the gene likely to harbor a germline mutation. Genetic sequencing and methylation studies
can be performed depending on results of the initial studies.
MSI analysis beyond HNPCC
Microsatellite instability has applicability outside of the detection of HNPCC. It has
been demonstrated that microsatellite unstable high tumors have an improved survival as compared with
stage matched stable cancers. In addition, recent studies, have suggested an association between low
level of microsatellite instability and poor cancer specific survival. Therefore, for prognostic
purposes it is useful to determine MSI status on all colorectal carcinomas. While many centers use
immunohistochemistry for all four proteins in lieu of MSI (assuming that tumors with any absent mismatch
repair protein are MSI positive), this cannot differentiate between tumors that are MSI high and MSI low
which may be important if they do indeed have a different prognosis. There remains controversy regarding
whether microsatellite unstable carcinomas respond differentially to some chemotherapy regimens as
compared with microsatellite stable carcinomas.
The detection of MSI is important to identify HNPCC and prognosis. Identification is based upon
history and laboratory testing. Histopathologic features in MSI colorectal can be recognized and may be
useful to identify patients who need further analysis, either with molecular studies or
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