Objective:To investigate the correlations of laminin subunit gamma 3 (LAMC3) expression with prognosis of ovarian cancer (OC).Methods:LAMC3 protein expression was measured using immunohistochemical streptavidin-peroxidase-biotin connection method (IHC). Gene expression and related clinical data in the cancer genome atlas (TCGA) cohort and clinical proteomic tumor analysis consortium (CPTAC) were applied to analyse the correlation between gene and protein expressions and clinical outcomes. Correlations between LAMC3 and clinicopathological factors were evaluated using the Pearson χ2 test (2-sided). The probability of survival and significance was calculated using the Kaplan-Meier plot. The functional clustering of biological pathways enriched from co-expressed genes of LAMC3 was used to explore the possible mechanisms that LAMC3 might contribute to poor prognosis. Results:Based on the IHC results of 216 OC tissues or ovaries (including 208 tumors and 8 normal tissues) and 51 OC tissues (including 24 chemotherapy-resistant and 27 sensitive tissues), and the protein expression data from CPTAC (including 100 primary tumors and 25 normal tissues), the results showed that the protein expression of LAMC3 was significantly decreased in OC tissues compared with normal, decreased in advanced-stage tissues compared with early-stage tissues, and decreased in drug-resistant tissues compared with sensitive tissues (all P<0.05). Furthermore, low expression of LAMC3 protein was significantly associated with poor disease-free survival (DFS) and overall survival (OS) in 51 OC tissues ( P<0.01), consistent with the results that the low levels of LAMC3 mRNA predicted short DFS and OS in 489 OC tissues of the TCGA cohort ( P<0.05). The results suggested that low expression of LAMC3 might be the adverse factors for OC development, such as drug resistance and advanced tumors, and might be a risk indicator for prognosis. Moreover, functional clustering of biological pathways enriched from the co-expressed genes of LAMC3 in TCGA ovarian cohort indicated that LAMC3 potentially involved in regulation of OC via oncogene-pathways such as Ras associated protein 1 (Rap1), mitogen-activated protein kinase (MAPK), Ras and cell adhesion-related pathways such as extra cellular matrix (ECM)-receptor interaction and focal adhesion. It indicated that LAMC3 might contribute to short survival and tumor progression by regulation of the above pathways. Conclusion:Low expression of LAMC3 is related to poor prognosis and malignant progression in OC, and thus it is expected to be a new prognostic marker and therapeutic target for clinical treatment.