The numeral of the metaplastic patients in the current series is 135 throughout a 10-year period which is higher than the numbers conveyed by other authors in the literature during a longer period, e.g., Jung et al. [9] described 35 cases during eight years; Chen et al. [13] and Aydiner et al. [14] reported 46 and 54 patients, respectively, through an era of 22 years; Cimino-Mathews et al. [28] described 45 cases over 14 years; and El Zein et al. [29] reported an analysis of 46 patients throughout 22-year period. The sample size in the current series is nearly similar to Tadros et al. [30] who described 132 cases but through a longer period of 23 years and faintly lower than Corso et al. [16] who reported 153 patients in an era of 22 years.

The median age in the present study was 52 years, near to what was previously reported [13, 16, 29, 31] and almost a decade younger than the authors stated [32, 33]. This inconsistency is almost due to differences in sample size and patient characteristics. Most patients were postmenopausal at diagnosis, which concurs with preceding results [16, 30, 32,33,34]. MRM was the most commonly employed curative surgery that corresponds with other reports [13,14,15, 29, 31, 33], a finding that could be explained by that as MetBC is one of the most aggressive pathologies with well-known resistance to neoadjuvant standard chemotherapy regimens with consequent low clinical downstaging rates; most surgeons opt to perform a radical surgery rather than to go for breast conservation. Despite less than a third of our cohort (28.9%) underwent BCS, the latter showed significantly superior OS on univariate analysis (p < 0.001), and as 92.3% of those patients received postoperative radiation therapy, we do assume similarity to the results of Zhang et al. [35] and Xia L-Y et al. [36] who described that MetBC patients subjected to BCS, and radiation therapy showed significantly better OS than those who underwent a mastectomy.

MetBC has low predilection for axillary nodal spread; this feature was depicted in our series as the major section (57.1%) of patients who underwent curative surgery had pN0. Pathological T2 and TNM stage 2 were prevalent in around half of the cases, 52 and 49%, respectively, typically matching other previous reports [9, 14, 15, 29, 32,33,34]. Initially, metastatic disease was diagnosed in 8.1% of our cohort, almost similar to Jung et al. [9] who reported 8.6%, and more or less double of what was stated by Cimino-Mathews et al. [28] and Takla et al. [33] who confirmed 4 and 3%, respectively. The lung was the commonest locality of spread either initially or on the subsequent development of recurrence, in agreement with the findings in [33].

Classically consistent with earlier reports demonstrating that MetBC is mostly TNBC [9, 13, 15, 16, 28, 30,31,32,33], two-thirds of our cohort (66%) had TN molecular subtype, when we compared the latter to the non-TN cases (34%); we could not elicit any statistically significant difference regarding the multiple clinicopathologic entities, treatment given, pathological response to NACT, or the event of recurrence between the two groups. Nevertheless, harboring a TN subtype was an independent worse prognostic element for both DFS and OS on MVA. Other studies explored the differences in survival between MetBC and non-metaplastic TNBC; the former had significantly inferior OS than the latter [9, 14, 29, 31, 34, 37]. These findings could be attributed to that the metaplastic pathology per se is a landmark for violence and aggression even when compared to the worst molecular subtype of the conventional IDC (TN).

Two other pathologic features could contribute to the harshness of this tumor: the high both histologic grade and proliferation index; GIII tumors were dominant in 83.7% in the current work, which coincides with the findings in [9, 14, 16, 28,29,30, 32] and an elevated median Ki-67 index in our patients of 45% (range: 10–88), in the work of Aydiner et al. [14]; a remarkably higher median of 70% was reported; moreover, in the results of Corso et al. [16] and Song et al. [31], 93.5 and 90% of their cohorts had levels ≥ 20 and ≥ 14%, respectively.

Squamous cell carcinoma was the main metaplastic histological subtype encountered in almost three-quarters of the current series (74.8%), analogous to previous results reported [9, 16, 32, 33]. Meanwhile, the mixed histology variant was dominant in Chen et al. [13] and Cimino-Mathews et al. [28]. Furthermore, the spindle cell variety was prevalent in [15, 38]. The latter histology was depicted in only 7.4% of our cases; nonetheless, it demonstrated significantly worst DFS and OS compared to other metaplastic varieties on univariate analysis, nearly similar to the conclusions stated by Song et al. [31] and Rakha et al. [38], the latter author documented that the matrix-producing subtype was related to the best survival. On the other side, the results of Tadros et al. [30] showed that squamous carcinoma and heterologous mesenchymal entities were linked with the poorest and best 5-year OS, respectively. The mixed metaplastic kind was correlated with worse DFS and OS in MVA in the work of Takla et al. [33]; however, the metaplastic subtype showed no significant impact on survival in the work of Corso et al. [16]. Accordingly, no definite solid conclusion regarding the best and worst metaplastic subtype so far could be postulated. However, factors other than the latter mostly motivate each tumor’s behavior, e.g., molecular and genetic aberrations, patient, and tumor characteristics.

Forty-one (30.3%) of our patients received NACT. Other authors also confirmed that minor fractions of their cohorts who received preoperative chemotherapy compared to adjuvant chemotherapy [13,14,15,16, 28,29,30, 32, 33], and combination regimens of anthracycline and taxanes were the most common type employed in almost two-thirds of those patients similar to [28, 39]; the majority (83%) of them had moderate and significant residual tumor burden (RCB-II & III) after NACT with only 3 cases (7.3%) who achieved pCR (RCB-0). Our findings of inadequate response to NACT are entirely matching other former studies and further support the concept of resistance of this tumor to conventional chemotherapy, as the pCR rate was 0% [14,15,16], 6% [39], 9.8% [37], 10% [12, 30], 17% [28], and 39% [32]. Interestingly, our univariate analysis showed that patients who received NACT had worse DFS and OS than those who did not (p = 0.01 & 0.02, respectively); nearly identical to what was described by Aydiner et al. [14], we could refer this result to that majority of patients subjected to NACT had a more advanced local disease and the response to chemotherapy was absolutely poor in the main bulk of those patients (83%). The study of Haque et al. [37] emphasized the significance of achieving pCR in this unique tumor, as MetBC patients who attained pCR had meaningfully greater 5-year OS than those with residual disease after NACT (p < 0.001), and fascinatingly, there was an identical survival outcome of the former cohort when compared to IDC patients with pCR (p = 0.99), the latter finding persisted even after splitting IDC patients to diverse molecular subtypes (TN, HER2-enriched and luminal with p-values: 0.91, 0.57 and 0.99, respectively). Adjuvant chemotherapy was employed in 59.3% of our series; the combinations of anthracyclines and taxanes were the most popular, similar to [14, 15, 28, 31]. Adjuvant chemotherapy was associated with significantly longer DFS and OS in univariate analysis (p < 0.001 & 0.019, respectively), approximately compatible with other results [28, 38, 40].

The 5-year DFS in the present study was 56.4% higher than what others described [9, 29, 31] and slightly lower than [15, 28, 33], whereas the 5-year OS in the current series was 57.6% near what was reported by [31, 33, 34] and lower than in [9, 14, 15, 28, 29, 32, 39], these discrepancies in survival figures are mostly due to differences in sample size, patients’ characteristics (most of the studies exclude initially metastatic patients) and follow-up durations. Our MVA results were comparable to other previous reports as high pT stage ( ≥ 3) was an independent prognostic factor for worse both DFS and OS, exactly concurring with previous results [