Numerous studies have shown that cancer development and metastasis formation are complex processes which involve not only cancer cells but also their interaction with selected components of tumor stroma. According to the seed and soil hypothesis, a permissive microenvironment (soil) facilitates growth of metastatic cancer cells (seed) in secondary sites. It was shown that stromal components (including cancerassociated fibroblasts, CAFs) can travel together with metastatic cells from the primary to secondary site. Moreover, co-traveling stromal cells can increase the viability of circulating metastatic cancer cells and provide them with an early growth advantage (1). It was also shown that CAFs promote tumor invasion by exerting a physical force on cancer cells, enabling them to escape from the primary site (2) . The identification of CAFs in peripheral blood from patients with metastatic breast cancer confirms the hypothesis suggesting co-travel of stromal and cancer cells during formation of metastases (3).In vitro studies and research based on animal models suggest a very important role of the cancer stroma in tumor progression (1, 4). The above phenomena were confirmed by studies in which the following stroma-related parameters were found to be of prognostic significance: (i) tumor-tostroma ratio (5-7); (ii) the type of tumor stroma (fibroblastdominant vs. lymphatic-dominant vs. collagen-dominant) (8-10); (iii) the presence of podoplanin-positive CAFs (ppCAFs) (11)(12)(13)(14) . Furthermore, it was suggested that CAFs might contribute to: (i) tumor initiation; (ii) proliferation, migration and invasiveness of cancer cells; (iii) tumor angiogenesis/lymphangiogenesis; (iv) tumor-induced inflammation; (v) metabolic reprogramming of the tumor microenvironment; and (vi) therapeutic resistance (4). Among many CAF-related proteins, podoplanin is one of the most intensively studied (8,9,(15)(16)(17) . Among breast cancer immunophenotypes, the human epidermal growth factor receptor 2 (HER2)-overexpressing subtype is the one in which ppCAFs were found to be relatively frequent (11).This prompted us to analyze: (i) the status of ppCAFs in primary tumor and paired synchronous lymph node metastases (LNMs); (ii) relation between ppCAFs in tumor