Background: Breast carcinoma is a malignancy that occurs from breast cells that grow and continue to proliferate uncontrollably. Mucin 1 (MUC1) has become a topic of interest in cancer treatment due to its upregulation, which affects the invasion, proliferation, and survival of tumor cells, by reducing cell-cell adhesion and extracellular cell-matrix adhesion. Objective: To analyze the correlation between the immunohistochemical expression of Mucin 1 (MUC1) with histopathological grading and molecular subtypes in invasive breast carcinoma. Methods: Formalin-fixed tissue paraffin blocks from 42 patients with invasive breast carcinoma were used as research samples and Mucin 1 (MUC1) immunohistochemical staining was assessed. The correlation between Mucin 1 (MUC1) expression and histopathological grading and molecular subtypes was analyzed by statistical tests using the SPSS program. Results: Of the 42 samples studied, for the age group, the most found were in the age group 40-49 years and the age group 50-59 years (each with 35.7%), while the age group 20-29 years was the least (2.4%). The most histopathological subtypes were invasive carcinoma of no special type (85.7%), with grade 2 being the most common (42.8%). The most common molecular subtype was luminal B (40.5%). Mucin 1 (MUC1) was expressed in 73.8% of invasive breast carcinoma specimens. Conclusion: There is a significant unidirectional correlation between the immunohistochemical expression of Mucin 1 (MUC1), either with histopathological grading or with molecular subtypes in invasive breast carcinoma (p-value were 0.027 and 0.010, respectively).