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Aim:The purpose of this study is to evaluate the prevalence of the immunohistochemical subtypes of breast cancer among Lao women by using immunohistochemistry (according to the St. Gallen 2017 guidelines) and to study their correlation to clinicopathological features in order to help guide better treatment plans for patients. Materials and methods:Formalin-fixed and paraffin embedded tissue blocks of 76 cases of primary invasive breast cancer were retrieved from the University of Health Sciences, Vientiane, Lao PDR, from 2013 to 2016. Patients’ information and previous histological reports were reviewed. Immunohistochemistry was done using antibodies against estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2/neu) and Ki-67 (MIB-1). Results:The mean age of the patients was 49 years, and the major histologic type was invasive ductal carcinoma, NOS (90.7%). The proportion of each subtype was hormone receptor-positive and HER2-negative, 44.7%; hormone receptor-positive and HER2-positive, 3.9%; hormone receptor-negative and HER2-positive, 13.2%; and triple-negative, 38.2%. ER was positive in 40.8% of the cases, while PR was positive in 47.4%. More than half of the cases were poorly differentiated cancer (65.8%), followed by moderately differentiated (34.2%). Tumors presented with pT2 (60.5%), followed by pT3 (25.0%) and pT4 (7.9%). Conclusion:Breast cancer among Lao women is characterized by a large percentage of the triple-negative subtype that is less susceptible to hormonal treatments. The empirical treatment with tamoxifen should be reconsidered since it would be less effective to these patients. More importantly, basic pathology services should be the first requirement in Lao PDR in order to provide adequate care.

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Purpose Three main treatment markers—estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2 (HER2) —are not routinely tested as a result of a lack of infrastructure of health care facilities. Quality control with which to validate these tests is also not available, and patients or their families have to pay for additional examination cost. Without hormonal receptor and HER2 status, treatment decisions are based on clinical finding; therefore, it is almost impossible to select patients who will benefit from therapy. Currently, none of the related research has ever been published in Lao People’s Democratic Republic. Methods From 2013 to 2016, formalin-fixed, paraffin embedded tissue blocks of 76 patients with primary breast cancer were retrieved at the University of Health Sciences (Vientiane, Lao People’s Democratic Republic). Patient information and previous histologic reports were reviewed. Immunohistochemistry was performed using antibodies against estrogen receptor, progesterone receptor, HER2/neu, and the protein encoded by the MKI67 gene (MIB-I). Results Mean age of patients was 49 years, with a majority of histologic type of invasive ductal carcinoma, not otherwise specified (90.7%). Proportions of each subtype were as follows: hormone receptor positive and HER2 negative, 44.7%; hormone receptor positive and HER2 positive, 3.9%; hormone receptor negative and HER2 positive,13.2%; and triple negative, 38.2%. Of patients, 40.8% were estrogen receptor positive and 47.4% were progesterone receptor positive. More than one half had poorly differentiated cancer (65.8%), followed by moderately differentiated cancer (34.2%). Tumors presented with pT2 (60.5%), followed by pT3 (25.0%) and pT4 (7.9%). Conclusion Breast cancer among Lao women is characterized by a large percentage of the triple-negative subtype as well as by being less susceptible to hormonal receptors. Most of our patients presented with locally advanced stage. HER2-positive and triple-negative breast cancer must be further investigated. To provide adequate care, basic pathology services should be the first requirement in Lao People’s Democratic Republic. Our findings could provide fundamental, useful data for a national policy to control breast cancer in the future. AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST The following represents disclosure information provided by authors of this manuscript. All relationships are considered compensated. Relationships are self-held unless noted. I = Immediate Family Member, Inst = My Institution. Relationships may not relate to the subject matter of this manuscript. For more information about ASCO's conflict of interest policy, please refer to www.asco.org/rwc or ascopubs.org/jco/site/ifc . No COIs from the authors.