Background <p>Alterations in N-glycosylation are frequently observed in breast cancer metastasis but are not well understood. Recently, decreases in expression of the Golgi α-mannosidase I MAN1A1 have been linked to worse patient prognosis in breast cancer.</p> Methods <p>To examine MAN1A1 expression in breast cancer progression, we developed and conducted MAN1A1 immunostaining of breast cancer tissue microarrays (TMAs), which were analyzed using pathology-guided object classifiers, which identified normal breast epithelial cells, primary tumor cells, and metastatic tumor cells.</p> Results <p>MAN1A1 protein expression was significantly increased in primary tumor and local lymph node metastasis for a cohort of patients without distant metastases (<i>N</i> = 48). Changes in MAN1A1 protein expression along the metastatic path were context-dependent, as well as associated with survival for a rare, limited cohort of terminal metastatic breast cancer patients (<i>N</i> = 16). For these patients, an increase in MAN1A1 expression from normal breast to primary tumor was concomitant with decreased survival time (<i>p</i> = 0.032, hazard ratio = 2.68), as was a decrease in MAN1A1 expression from primary tumor to metastasis (<i>p</i> = 0.0018, hazard ratio = 3.45).</p> Conclusion <p>In our pilot study, MAN1A1 protein expression is a significant actor in progression along the metastatic path, supporting further study into MAN1A1 as driver of breast cancer patient survival.</p>