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Breast cancer is the most prevalent malignancy among women worldwide, and the increasing number of survivors is due to advances in early diagnosis and treatment efficacy. Consequently, the risk of developing contralateral breast cancer (CBC) among these survivors has become a concern. While surgical intervention with lumpectomy is a widely used primary approach for breast cancer, post-operative breast asymmetry is a potential concern. Many women opt for symmetrizing reduction procedures to improve aesthetic outcomes and quality of life. However, despite careful radiological screening, there is a chance of accidentally finding CBC. To address this, tissue excised during symmetrizing surgery is examined pathologically. In some cases, CBC or in situ lesions have been incidentally discovered in these specimens, prompting a need for a more thorough examination. Resection in pieces and the absence of surgical marking and pathological inking of the margin have made it challenging to precisely identify tumor location and assess tumor size and margin status, hampering adjuvant treatment decisions. A new protocol introduced in July 2022 aims to enhance the precision of CBC diagnosis, allowing for tailored treatment plans, including re-excision, systemic adjuvant therapy, or radiation therapy.

Patients with advanced triple-negative breast cancer (TNBC) benefit from treatment with atezolizumab, provided that the tumor contains ≥1% of PD-L1/SP142-positive immune cells. Numbers of tumor-infiltrating lymphocytes (TILs) vary strongly according to the anatomic localization of TNBC metastases. We investigated inter-pathologist agreement in the assessment of PD-L1/SP142 immunohistochemistry and TILs. Ten pathologists evaluated PD-L1/SP142 expression in a proficiency test comprising 28 primary TNBCs, as well as PD-L1/SP142 expression and levels of TILs in 49 distant TNBC metastases with various localizations. Interobserver agreement for PD-L1 status (positive vs. negative) was high in the proficiency test: the corresponding scores as percentages showed good agreement with the consensus diagnosis. In TNBC metastases, there was substantial variability in PD-L1 status at the individual patient level. For one in five patients, the chance of treatment was essentially random, with half of the pathologists designating them as positive and half negative. Assessment of PD-L1/SP142 and TILs as percentages in TNBC metastases showed poor and moderate agreement, respectively. Additional training for metastatic TNBC is required to enhance interobserver agreement. Such training, focusing on metastatic specimens, seems worthwhile, since the same pathologists obtained high percentages of concordance (ranging from 93% to 100%) on the PD-L1 status of primary TNBCs.