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The International Journal of the Royal Society of Thailand
Volume XI - 2019

(Korphaisarn et al. 2019). How these discrepancies translate to clinical implication
remain to be elucidated.

Breast Cancer
Breast cancer is the most common cancer in female worldwide. It is

categorized into 3 main subtypes based on expression of cell surface receptors.
Hormone-receptor positive breast cancer is the most common group (60%) with
expression of estrogen receptor (ER) and progesterone receptor (PR) on cancer cells.
Approximately 15% of breast cancer showed overexpression of human epithelial
growth factor receptor-2 (HER2) on cell surface. Triple negative breast cancer
(TNBC) accounts for the remaining 15–20% of breast cancer. TNBC patients are
not eligible for effective selective hormonal modulator or anti-HER2 treatments
because of the absence of both targets and usually carry worse prognosis. TNBC
is a heterogeneous disease with marked variation in clinical characteristics and
response to chemotherapy treatment. Studies on TNBC genome confirmed that
mutational profiles in TNBC are diverse and patient’s ethnicity could have
significant role (Ademuyiwa et al. 2017). A study of breast cancer patients in
Thailand also displayed distinct genomic profile in Thai TNBC which several
cancer genes were more frequently mutated than in Western TNBC patients
(Niyomnaitham et al. 2019). The genomic heterogeneity between Caucasian and
Thai TNBC could lead to different therapeutic approach between 2 populations.

Besides somatic mutations in tumor tissue, breast cancer is also associated
with inherited cancer syndromes caused by germline mutations in tumor
suppressor genes. The most well-known breast cancer susceptibility genes are
BRCA1 and BRCA2. Both genes account for 75% of identified pathogenic/likely
pathogenic mutations in breast cancer susceptibility genes. Due to high lifetime

risk of developing breast and ovarian cancers among BRCA1 and BRCA2 mutation
carriers, standard guidelines for genetic testing, cancer screening and prevention
do exist. It is noted on many studies that Asian individuals with clinical suspicion
of hereditary breast-ovarian cancer had high prevalence of BRCA1 or BRCA2
mutations (Kim and Choi 2013). The reason remains unknown. It is possible that
the disease is less contributed by environmental and hormonal factors among
Asian patients so genetic risk could confer more greatly to cancer susceptibility.

50 Cancer Precision Medicine and Ethnic Diversity

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