Infiltrating metastatic ductal carcinoma initially presenting as axillary lymph node metastases diagnosed with PET/CT and MRI: case report and brief review of occult breast carcinoma.

INTRODUCTION: The concept of occult breast carcinoma (OBC) was first described in 1907 by Halsted, who described this type of breast cancer to arise from small, undetectable tumours in the breast that had already metastasized to the lymph nodes. Although the breast is the most likely site for the primary tumour, non-palpable breast cancer presenting as an axillary metastasis has been reported, but with a low frequency of less than 0.5% of all breast cancers. OBC represents a complex diagnostic and therapeutic dilemma. Considering its rarity, clinicopathological information is still limited.

CASE REPORT: A 44-year-old patient presented to the emergency room with an extensive axillary mass as the first manifestation. Conventional evaluation of the breast with mammography and ultrasound was unremarkable. However, a breast MRI confirmed the presence of conglomerate axillary nodes. A supplementary whole-body PET-CT established the axillary conglomerate with a malignant behaviour with SUVmax of 19.3. The primary tumour was not detected in the breast tissue of the patient, confirming the diagnosis of OBC. Immunohistochemical results showed negative receptors for estrogen and progesterone.

CONCLUSION: Although OBC is a rare diagnosis, its existence is a possibility in a patient with breast cancer. Mammography and breast ultrasound with unremarkable findings but with high clinical suspicion should be supplemented with additional imaging methods, such as MRI and PET-CT, emphasizing the appropriate pre-treatment evaluation.