Mixed Metaplastic Carcinoma of the Breast: A Case Report
Authors: Tower Amelia , Hughes Jonathan , Moore Lauren , Srivast Kumaraman 
Published: December 2022

Abstract
Background:

Metaplastic carcinoma (MpBC) of the breast is an exceedingly rare group of malignancies that accounts for 0.2–5% of all breast cancers. As such, there is no current consensus on standardized treatment, and physicians often rely on case reports to help guide their understanding of this cancer as well as help formulate the most optimal treatment options for their patients. The following case consists of metaplastic carcinoma of the breast with biopsy proven squamous axillary disease. This case report includes the multidisciplinary treatment of MpBC which consisted of neoadjuvant chemotherapy that resulted in a near complete pathologic response on surgical pathology. Thus, we present a rare case of mixed metaplastic breast carcinoma with unusual metastatic disease and confirming the utility of treatment of neoadjuvant chemotherapy in this population of patients.

Case presentation:

A 68 year-old Caucasian woman with no significant past medical or family history discovered a lump incidentally in her left breast with no associated signs or symptoms. The patient had received no annual mammogram screenings and did not do self-examinations regularly. The patient’s initial diagnostic imaging revealed a 4.6 cm irregular mass at 11:00 categorized as a BI-RADS 5 as well as a suspicious enlarged axillary lymph node and an area of 2.5 cm of heterogeneous calcifications in the 3 o'clock position. She then subsequently underwent an ultrasound-guided core needle biopsy of the left breast 11:00 lesion as well as axillary lymph node and also had a stereotactic core needle biopsy of the calcifications. The 4.6cm lesion was revealed to be infiltrating ductal carcinoma with a minor squamous component, mixed metaplastic carcinoma, that was strongly ER (100+)/PR (100+) positive, HER-2/Neu (2+ equivocal on immunohistochemistry) negative on fluorescence in situ hybridization (FISH). The 2.5cm calcifications were revealed to be ductal carcinoma in situ. No prognostics were able to be performed due to the scant sample size. The lymph node biopsy revealed metastatic keratinizing squamous cell carcinoma with a minor component resembling the breast tumor that was weakly positive for ER (5+), negative for PR, equivocal per IHC, and negative on FISH. The patient completed neoadjuvant chemotherapy, and based on interval physical exams and diagnostic imaging, she had an excellent response. After multidisciplinary discussion and very thorough surgical counseling, the patient elected for breast conservation therapy and underwent a left wireless localized partial mastectomy of the biopsy proven carcinomas with a left targeted axillary dissection. The surgical pathology revealed a near complete pathologic response with only 8mm residual tumor remaining as well as a negative conversion of the clipped axillary node.
· Conclusions:
Due to advanced locoregional disease at the time of diagnosis, as well as historically poor responses to neoadjuvant chemotherapy, patients diagnosed with metaplastic breast carcinoma often proceed with invasive surgery as the initial treatment. This case, however, demonstrates the successful implementation for a very rare pathology with a near complete pathologic response to neoadjuvant chemotherapy. Therefore, this case demonstrates the utilization of neoadjuvant chemotherapy as the initial treatment in patients with metaplastic breast carcinoma.