Triple-negative apocrine carcinoma: A rare pathologic subtype with a better prognosis than other triple-negative breast cancers

Rare subtypes of triple negative breast cancer: Current understanding and future directions

Rare subtypes of triple-negative breast cancers (TNBC) are a heterogenous group of tumors, comprising 5-10% of all TNBCs. Despite accounting for an absolute number of cases in aggregate approaching that of other less common, but well studied solid tumors, rare subtypes of triple-negative disease remain understudied. Low prevalence, diagnostic challenges and overlapping diagnoses have hindered consistent categorization of these breast cancers. Here we review epidemiology, histology and clinical and molecular characteristics of metaplastic, triple-negative lobular, apocrine, adenoid cystic, secretory and high-grade neuroendocrine TNBCs. Medullary pattern invasive ductal carcinoma no special type, which until recently was a considered a distinct subtype, is also discussed. With this background, we review how applying biological principals often applied to study TNBC no special type could improve our understanding of rare TNBCs. These could include the utilization of targeted molecular approaches or disease agnostic tools such as tumor mutational burden or germline mutation-directed treatments. Burgeoning data also suggest that pathologic response to neoadjuvant therapy and circulating tumor DNA have value in understanding rare subtypes of TNBC. Finally, we discuss a framework for advancing disease-specific knowledge in this space. While the conduct of randomized trials in rare TNBC subtypes has been challenging, re-envisioning trial design and technologic tools may offer new opportunities. These include embedding rare TNBC subtypes in umbrella studies of rare tumors, retrospective review of contemporary trials, prospective identification of patients with rare TNBC subtypes entering on clinical trials and querying big data for outcomes of patients with rare breast tumors.

Apocrine adenocarcinoma of the breast: A rare special subtype with divergent theranostic markers

Carcinoma of the breast with apocrine differentiation also known as apocrine adenocarcinomas is special histological subtypes comprising approximately 1% of breast cancers. They are estrogen receptor/progesterone receptor-negative and androgen receptor-positive tumors having more than 90% population of tumor cells with apocrine morphology. We present a 49-year-old woman with a breast lump in the right upper outer quadrant clinically and radiologically diagnosed as malignancy and histologically proven as apocrine adenocarcinoma of the breast owing to the morphology comprising tumor cells having abundant granular cytoplasm, central to the eccentric nucleus and prominent nucleoli. On immunohistochemistry, it was a triple-negative tumor with AR positivity. As apocrine adenocarcinoma of the breast has an uncertain prognosis, variable HER2/neu overexpression, debatable responses to neoadjuvant therapy, and probable response to androgen therapy, the onus of diagnosing and reporting these tumors accurately lies with the pathologist. Moreover, as the presentation of these tumors is similar to invasive breast carcinoma, no special type but with potentially different and useful theranostic markers, an emphasis on specifying this histological subtype is becoming increasingly essential.

Disease Behavior and Treatment Response of Special Histological Types of Triple-Negative Breast Cancer

BACKGROUND

Special histological types (SHT) of triple-negative breast cancer (TNBC) are a heterogeneous group of rare poorly understood diseases. We aimed to evaluate the clinical features, treatment, and outcomes of patients with SHT of TNBC.

METHODS

We evaluated patients with a SHT of TNBC treated in a cancer center between 2009 and 2020. The endpoints were characterization of clinical and pathological features, pathologic complete response (PCR) rate after neoadjuvant chemotherapy, disease-free survival (DFS), progression-free survival, and overall survival (OS).

RESULTS

The 132 patients included had the following histologies: metaplastic (n=71), medullary pattern (n=14), lobular (n=12), adenoid cystic (n=12), apocrine (n=10), and others (n=13). Metaplastic, lobular, and medullary pattern tumors had higher grade (66.6-85.7% grade 3); adenoid cystic and apocrine had mainly grade 1-2 (70-83.3%). Metaplastic and lobular carcinomas had higher disease stages (47.8% and 58.2% stages III-IV). PCR rates were 10.3% for metaplastic and 33.3% for lobular carcinomas, with 5-year DFS rates of 56% and 51.4%. Medullary pattern carcinomas had a great response to treatment, with PCR rate of 100%, and 5-year DFS rate of 92.8%. Apocrine carcinomas also had favorable prognosis, with no recurrence after early disease treatment, and 5-year DFS rate of 83.3%. Adenoid cystic carcinomas had intermediate prognosis, with 5-year DFS rate of 66.6%.

CONCLUSION

SHT of TNBC encompasses heterogeneous malignancies with distinct behaviors. Lobular and metaplastic carcinomas showed high aggressiveness and poor treatment response, while medullary pattern and apocrine carcinomas had favorable outcomes. Treatment strategies focus on molecular features of each of these diseases are warranted.

HER2-positive apocrine carcinoma of the breast: a population-based analysis of treatment and outcome

PURPOSE

Apocrine carcinoma of the breast (APO) expresses HER2 in 30-50% of cases. This study explored the clinicopathological features and outcome of HER2+/APO and matched HER2+/NST cohort.

METHODS

We used the SEER database to explore the cohorts. Univariate and multivariate analyses were used to assess the survival. Based on ER and PR [steroid receptors/SR/] and HER2 status, we divided the cohorts to match the intrinsic molecular subtypes for comparisons.

RESULTS

We retrieved 259 cases of HER2+/APO. Most HER2+/APO were SR negative (65%). HER2+/APO were more prevalent in the 80+ age group (24.7% vs. 15.7%, p < 0.001). HER2+/SR-/APO had a significantly lower histological grade than the HER2+/SR-/NST (p < 0.001). Breast cancer-related deaths were more prevalent in HER2+/NST (7.8% vs. 3.9%, p = 0.019). This was particularly evident between SR- subgroups (10.4% in HER2+/SR-/NST vs. 4.2% in HER2+/SR-/APO, p = 0.008) and was reaffirmed in breast cancer-specific survival in univariate analysis (p = 0.03). Other than race and SR status, HER2+/APO subgroups did not differ in clinicopathological parameters.

CONCLUSIONS

Our study confirms the rarity of the APO and reveals that SR status in APO does not affect these patients' prognosis. HER2+/APO tumors tend to have a less aggressive phenotype and a more favorable outcome despite a markedly lower ER/PR positivity.

Subclassifying triple-negative breast cancers and its potential clinical utility

The molecular subtyping of triple-negative breast cancer (TNBC) is critical to guiding individualized patient treatment. In this study, we sought to characterize the clinicopathologic features of TNBC subtypes and to identify correlates of patient survival in an effort to provide a robust foundation for treatment planning. We additionally assessed PD-L1 expression in Chinese TNBC patients and evaluated the relationship between such expression and immunotherapeutic treatment outcomes. Based on analyses of histologic characteristics including apocrine differentiation, tumor-infiltrating lymphocytes, and metaplastic features, we selected immunohistochemical (IHC) markers including CD8, FOXC1, and AR for use in classifying TNBC cases. Associations between these subtypes and a range of clinicopathologic characteristics were evaluated. We classified a cohort of 93 TNBC patients into individuals with luminal androgen receptor (LAR), immunomodulatory (IM), basal-like immune-suppressed (BLIS), and mesenchymal (MES) tumor subtypes (23, 24, 39, and 7 cases, respectively). PD-L1 positivity was observed in 49.6% of cases and was more common in individuals with IM subtype disease. Mismatch repair deficiency (dMMR) was observed in just one patient. Significant differences in histologic grade, pT stage, lymphocyte distribution patterns, large scarring areas without cells in tumor of central (central scar), and PD-L1, P53, and Rb status were observed among these TNBC subtypes, whereas no such differences were observed with respect to age, invasion pattern, or pN stage. Rates of disease progression were higher at the 40-50 month follow-up time point, but there were no significant differences in recurrence-free survival or breast cancer-specific survival among these subtypes. IHC markers associated with clinicopathologic characteristics represent a powerful approach to TNBC molecular typing, providing a foundation for precision patient treatment. PD-L1 expression may represent a relevant factor in TNBC patient immunotherapeutic treatment planning, whereas dMMR is not likely to be of substantial value when evaluating immunotherapeutic efficacy in these patients.

Triple-Negative Apocrine Breast Carcinoma Has Better Prognosis despite Poor Response to Neoadjuvant Chemotherapy

Apocrine carcinoma is a rare subtype of invasive ductal breast cancer that shows apocrine differentiation and largely triple-negative immunohistology. Triple-negative breast cancers are known to have more aggressive clinical courses. However, unlike most other subtypes, it is reported that triple-negative apocrine carcinoma (TNAC) has a better prognosis. Due to the scarcity of reported studies, our knowledge regarding its clinical behavior, prognosis and response to therapy is very limited. In this study, we retrospectively retrieved 41 triple-negative apocrine carcinoma cases from our breast cancer database, with an average follow-up of 32.8 months. It was found that TNAC had a poorer response to neoadjuvant therapy but a better prognosis than other nonapocrine types of triple-negative breast cancer. Meanwhile, TNAC has a low proliferative nature, as indicated by its low Ki-67 index. An updated analysis of the Surveillance, Epidemiology, and End Results database showed that chemotherapy did not improve breast-cancer-specific survival in TNAC patients. Our results suggest that TNAC is a special subtype of triple-negative breast cancer with a better short-term prognosis despite poor response to neoadjuvant chemotherapy.

Low-risk triple-negative breast cancers: Clinico-pathological and molecular features

Triple-negative breast cancers (TNBC) comprise biologically and clinically heterogeneous diseases characterized by the lack of hormone receptors (HR) and HER2 expression. This subset of tumors accounts for 15-20% of all breast cancers and pursues an ominous clinical course. However, there is a spectrum of low-risk TNBCs with no/minimal metastatic potential, including the salivary gland-type tumors, those with extensive apocrine differentiation and/or high tumor-infiltrating lymphocytes, and small-sized, early-stage (pT1a/bN0M0) TNBCs. De-escalating the treatment in low-risk TNBC, however, is not trivial because of the substantial lack of dedicated randomized clinical trials and cancer registries. The development of new diagnostic and/or prognostic biomarkers based on clinical and molecular aspects of low-risk TNBCs would lead to improved clinical treatment. Here, we sought to provide a portrait of the clinicopathological and molecular features of low-risk TNBC, with a focus on the diagnostic challenges along with the most important biological characteristics underpinning their favorable clinical course.

An Update on the Molecular and Clinical Characteristics of Apocrine Carcinoma of the Breast

Apocrine carcinoma of the breast is a rare malignancy. According to 2019 WHO classification, apocrine cellular features and a characteristic steroid receptor profile (Estrogen receptor (ER)-negative and androgen receptor (AR)-positive) define apocrine carcinoma. Her-2/neu protein expression is reported in ∼30-50% of apocrine carcinomas, while NGS analysis showed frequent PIK3CA/PTEN/AKT and TP53 mutations Followed by deregulation in the mitogen-activated protein kinase pathway components (mutations of KRAS, NRAS, BRAF). A recent miRNA study indicates various miRNAs (downregulated hsa-miR-145-5p and upregulated 14 miRNAs such as hsa-miR-182-5p, hsa-miR-3135b, and hsa-miR-4417) may target the commonly altered pathways in apocrine carcinomas such as ERBB2/HER2 and mitogen-activated protein kinase signaling pathway. Although AR expression is a hallmark of apocrine carcinoma, little is known regarding the efficacy/resistance to antiandrogens. Success of bicalutamide, a non-steroidal anti-androgen, was reported in a case of Her2-negative apocrine carcinoma. Two recent studies, however, described presence of anti-androgen resistance biomarkers (a splice variant ARv7 and AR/NCOA2 co-amplification) in a subset of AR+ apocrine carcinomas, cautioning the use of anti-androgens in AR+ triple-negative breast carcinomas. Apocrine carcinomas rarely show biomarkers predictive of response to immune checkpoint inhibitors (PD-L1 expression, MSI-H status, and TMB-high). Therefore, a comprehensive cancer profiling of apocrine carcinomas is necessary to identify potential therapeutic targets for a truly individualized treatment approach.

Triple-negative apocrine carcinoma as a rare cause of a breast lump in a Syrian female: a case report and review of the literature

Background

Apocrine carcinoma is a rare tumor that constitutes < 4% of all breast malignancies, characterized by the proliferation of large atypical cells with strictly defined borders, abundant eosinophilic cytoplasm, large nuclei, and prominent nucleoli in more than 90% of tumor cells. Triple-negative apocrine carcinoma is a rare molecular subtype that constitutes less than 1% of triple-negative breast cancers and is characterized by negative expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor, with positive expression of androgen receptor.

Case presentation

We report a case of a 45-year-old Syrian female who presented to our hospital due to a painless palpable mass in her left breast. Following physical and radiological examinations, an excisional biopsy was performed. Microscopic examination of the specimen followed by immunohistochemical staining revealed the diagnosis of a triple-negative apocrine carcinoma.

Conclusion

Triple-negative apocrine carcinoma is an extremely rare neoplasm that must be considered in the differential diagnoses of breast lesions through detailed clinical, histological, and immunohistochemical correlations. In our manuscript, we aimed to present the first case report of a Syrian female who was diagnosed with a triple-negative apocrine carcinoma, aiming to highlight the importance of detailed clinical, histological and immunohistochemical correlations with a detailed review of diagnostic criteria, molecular characteristics, and treatment recommendations.

Rare Breast Cancer Subtypes

PURPOSE OF REVIEW

Breast cancer is a collection of diseases including the more common invasive ductal and lobular carcinomas and rarer subtypes of breast cancer. This review summarizes the features of rare breast cancers.

RECENT FINDINGS

Each of the rare tumors has defined pathological and clinical features that impact treatment recommendations. In this review, we summarize these for each rare type of breast cancer and where available we include molecular features of each tumor. Rare subtypes of breast cancer each have unique features. In many cases, data is limited for the optimal treatment approaches.