Introduction
A rare entity, constituting 0.2-5% of the global breast cancer (BC) burden, metaplastic breast cancer (MpBC) [1].  MpBC represents a significant proportion of global BC mortality.
MpBC represents a group of mostly high-grade tumours, demonstrating at least two unique cellular types- characteristically epithelial and mesenchymal elements mixed with carcinoma of the usual kind [2]. These metaplastic changes represent a conversion from glandular breast tissue to non-glandular carcinomatous (squamous) and sarcomatous (spindle cell, chondroid, osseous, and rhabdoid cells) morphologies [3].
There can be high-grade variants with high metastasis potential or low-grade variants such as fibromatosis-like carcinoma and low-grade adenosquamous carcinoma (Fig 1).
The high-grade variants have a high likelihood of metastasis and are notoriously chemoresistant and aggressive [4]. The rarer low-grade variants have a relatively favourable prognosis as compared to the commoner high-grade subtypes [5].
These tumours are typically triple-negative [3,4]. There are however proteomic and genomic differences between conventional TNBC and MpBC. Spindle-cell carcinoma commonly expresses p63 and low-grade adenosquamous carcinoma show high rates of PIK3CA. Conventional TNBC have low PIK3CA expression. Osteoid and chondroid variants show increased SNail, BCL-2-like protein and Akt-1 pathway activity. In contrast to non-MpBC TNBC tumours, MpBC showed higher upregulation of epithelial-to-mesenchymal transition (EMT) and collagen genes, but downregulation of keratinization genes. These support the hypothesis that the histological, proteomic and genomic variations may contribute to the deadliness of these BC variants [6].
MpBC has a worse prognosis as compared to non-metaplastic triple-negative BC (TNBC). There is a shorter disease-free interval and overall survival with a double chance of recurrence [7]. Spindle cell differentiation has the worst 5-year survival at about 40% [6].
Here we report the case of a lady who presented with a locally advanced disease that was found to be metaplastic cancer on histology and is now 3 years disease free.