Introduction:
LS is an autosomal dominant inherited disorder with high penetrance that
places individuals at an increased risk for colorectal cancers at an
early age. 3% of colorectal cancers are attributable to LS. Individuals
with LS are at a 50-70% lifetime risk of developing colorectal cancers
and usually before 50 years old [1]. LS can also put individuals at
an increased risk for endometrial (40-60%), ovarian, stomach,
pancreatic, and urinary tract cancers. It is caused by a germline
mutation in the DNA mismatch repair genes MLH1, MSH2, MSH6, PMS2. In
some patients, it is also caused by a 3’end deletion of the EPCAM gene,
which leads to an epigenetic silencing of MSH2 gene. MLH1 and MSH2 genes
are most commonly mutated in LS patients accounting for
in MSH2) [1]. It is estimated 1 in 279 individuals in the United
States have a gene mutation associated with LS [2].
Screening for LS includes testing for microsatellite instability (MSI),
immunohistochemistry staining (IHC), and methylation/BRAF V600E testing
[2]. Screening should be offered to individuals who meet the
criteria for Amsterdam II criteria or revised Bethesda guideline (Fig. 1
and Fig. 2). Within LS, there are two variants, MTS and TS. MTS is
characterized by skin cancers (sebaceous or keratoacanthomas) in
association to colorectal cancer [3]. TS is characterized by primary
brain tumors (medulloblastomas, glioblastomas, ependymomas, and
astrocytomas) in association with colorectal cancer [4]. In this
study we discuss an atypical presentation of MTS.