Comparison of histomorphological and immunohistochemical analysis results routinely applied to tru-cut biopsy and mastectomy materials in invasive breast cancer

Aim: Breast cancer is the most frequently diagnosed malignancy in women worldwide and in Turkey and is one of the leading causes of cancer-related mortality. Tru-cut biopsy performed under ultrasonographic guidance plays a crucial role in identifying the histopathological and immunohistochemical characteristics of the tumor as a minimally invasive diagnostic method. However, due to the limited tissue sample and tumor heterogeneity, findings obtained from tru-cut biopsy may not always correspond completely with those from the surgical excision specimen. This study aimed to evaluate the concordance between tru-cut biopsy and surgical excision specimens in patients diagnosed with invasive breast cancer, in terms of histomorphological (tumor type, histological grade, Nottingham parameters) and immunohistochemical (ER, PR, HER2, Ki67) features. Additionally, the study examined whether this concordance differed between patients who received neoadjuvant therapy and those who did not. Methods: This retrospective and cross-sectional study included 206 cases diagnosed with invasive breast cancer between 2017 and 2023, who had both tru-cut biopsy and surgical excision specimens available. Tumor type, histological grade, Nottingham grading system parameters (tubule formation, nuclear pleomorphism, mitotic index), and immunohistochemical markers (ER, PR, HER2, Ki67) were compared between the two specimen types. Based on the immunoprofile, molecular subtyping was also performed, and concordance between the biopsy and excision was assessed using Cohen's kappa (κ) statistic. Subgroup analyses included clinical factors such as tumor size and focality as well as neoadjuvant treatment status. Results: A total of 206 invasive breast cancer cases were included. Concordance between tru-cut biopsy and surgical excision was κ=0.74 for tumor type and κ=0.21 for histological grade. In patients receiving neoadjuvant therapy, these values decreased to κ=0.47 and κ=0.13, respectively. For Nottingham parameters, kappa values were κ=0.39 for tubule formation and κ=0.14 for nuclear pleomorphism. The kappa value for mitotic index was κ=0.04 and was not statistically significant. For immunohistochemical markers based on positivity/negativity, kappa values were κ=0.82 for ER, κ=0.66 for PR, and κ=0.53 for HER2. In the neoadjuvant therapy group, these values declined to κ=0.75, κ=0.59, and κ=0.43, respectively. For the Ki67 vi low/high classification, the general kappa value was κ=0.31, decreasing to κ=0.22 in the neoadjuvant group, and was not statistically significant. Concordance for molecular subtype classification was moderate (κ=0.47) and decreased in the neoadjuvant group (κ=0.39). Additionally, tumor focality and the size of the invasive tumor observed in the tru-cut biopsy specimens were found to significantly affect concordance for certain histomorphological and immunohistochemical parameters. Conclusion: This study revealed varying levels of concordance between tru cut biopsy and surgical excision specimens for histomorphological and immunohistochemical parameters. While high concordance was observed for tumor type and estrogen receptor (ER), moderate concordance was found for progesterone receptor (PR), HER2 status, and molecular subtype classification. Lower concordance was observed for histological grade, Nottingham parameters (tubule formation, nuclear pleomorphism, mitotic index), and Ki67. In cases with neoadjuvant therapy, the concordance was notably reduced, indicating the impact of treatment on tumor biology. Tumor focality and the size of the tumor in the biopsy specimen also influenced the level of concordance. These findings suggest that while tru-cut biopsy is a valuable tool in the preoperative diagnostic process, reassessment with surgical excision material is crucial, especially after neoadjuvant therapy or when biopsy representation is limited, to ensure accurate clinical decision-making. Keywords: Core-Needle Biopsy, Surgical Excision, Histomorphological Concordance, Immunohistochemical Markers, Breast Cancer, Neoadjuvant Therapy, Tru-Cut Biopsy