Immunohistochemically Defined Subtypes and Outcome of Apocrine Breast Cancer

Original Study

Immunohistochemically Defined Subtypes and Outcome of Apocrine Breast Cancer Silvia Dellapasqua,1 Patrick Maisonneuve,2 Giuseppe Viale,3 Giancarlo Pruneri,3 Giovanni Mazzarol,3 Raffaella Ghisini,1 Manuelita Mazza,1 Monica Iorfida,1 Nicole Rotmensz,2 Paolo Veronesi,4 Alberto Luini,5 Aron Goldhirsch,6,7 Marco Colleoni1 Abstract Pure apocrine carcinoma represents a distinct subtype of breast cancer and is associated with a worse outcome in terms of disease-free survival (DFS) if compared with invasive ductal carcinoma. Androgen receptor (AR) determination might have an important prognostic implication in apocrine carcinomas, and AR-targeted therapy should be further explored in these tumors. Background: Conflicting data are available in the literature on the outcome of invasive apocrine carcinoma (IAC), possibly related to a heterogeneous classification of these tumors. Patients and Methods: A series of 6899 consecutive patients with invasive ductal carcinoma (IDC) not otherwise specified and 72 patients with immunohistochemically defined IAC who received surgery at the European Institute of Oncology between 1997 and 2005 were included. We then explored patterns of recurrence of IAC according to 2 immunohistochemically defined tumor subtypes: pure apocrine carcinoma (estrogen [ER] and progesterone [PgR] receptor negative, and AR positive) and apocrine-like carcinoma (ER or PgR positive and AR negative). Results: The diagnosis of pure apocrine carcinoma was correlated with a worse outcome in terms of DFS (hazard ratio [HR] 1.7; 95% confidence interval [CI], 1.01-2.86; P ⫽ .0010) if compared with IDC, whereas IDC and apocrine-like breast cancers showed a similar outcome in terms of DFS and overall survival. Patients with pure apocrine carcinoma had an increased risk in contralateral breast cancer (HR, 4.12; 95% CI, 1.22-14; P ⫽ .02). Conclusion: Pure apocrine carcinoma represents a distinct subtype of breast cancer with a significantly worse DFS as compared with IDC. AR determination might have an important prognostic implication in IAC. Moreover, AR-targeted therapy should be further explored within these tumors. Clinical Breast Cancer, Vol. 13, No. 2, 95-102 © 2013 Elsevier Inc. All rights reserved. Keywords: Androgen receptor, Apocrine, Apocrine-like, Breast cancer

Introduction The choice of adjuvant systemic therapy for early breast cancer implies tailoring treatments to individual patients according to assessment of patient’s risk, comorbidities, and preference.1-3 Risk factors traditionally associated with an increased risk of relapse include nodal status, peritumoral vascular invasion, HER2 amplification/ overexpression, high grade, and high proliferation index.4-7

1 Research Unit in Medical Senology, Department of Medicine, European Institute of Oncology, Milan, Italy 2 Division of Epidemiology and Biostatistics, European Institute of Oncology, Milan, Italy 3 Division of Pathology and Laboratory Medicine, European Institute of Oncology and University of Milan, Milan, Italy 4 Integrated Breast Surgery Unit, European Institute of Oncology and University of Milan, Milan, Italy 5 Division of Senology, European Institute of Oncology, Milan, Italy 6 Department of Medicine, European Institute of Oncology, Milan, Italy

1526-8209/$ - see frontmatter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.clbc.2012.11.004

More recently, studies of DNA microarray profiling have led to the recognition that breast cancer is a heterogeneous entity at the molecular and genetic levels, and to the identification of different classes of invasive breast cancer with shared molecular features (luminal A and B, HER2, normal breast-like, and basal-like).8-12 Moreover, microarray-based methods have led to the development of molecular taxonomy and of prognostic ‘gene signatures.’13-17

7

Swiss Center for Breast Health, Sant’Anna Clinic, Lugano-Sorengo, Switzerland

Submitted: Jul 13, 2012; Revised: Oct 1, 2012; Accepted: Nov 8, 2012; Epub: Dec 14, 2012 Address for correspondence: Silvia Dellapasqua, MD, Research Unit in Medical Senology, Department of Medicine, European Institute of Oncology, Via Ripamonti 435, 20141 Milan, Italy E-mail contact: [email protected]

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Apocrine Breast Cancer and Immunohistochemical Subtypes Table 1 Characteristics of Women With Apocrine and Ductal Breast Cancer Characteristics

Total

All Patients

6971

Immunophenotypic Profilea

Histologic Subtype Ductal

Apocrine

6899

72

P

Pure Apocrine

Apocrine-Like

44

25

P

Age Group ⬍ 35

327

325

2

0

1

35-49

2612

2593

19

11

7

50-69

3378

3336

42

25

16

ⱖ 70

654

645

9

8

1

1693

1680

13

5

6

.04b

.11b

Tumor Size ⱕ 1 cm 1-2 cm

2956

2925

31

20

11

2-5 cm

2049

2024

25

19

6

0

2

25

17

19

6

0

2

⬎ 5 cm

211

208

3

Unknown

62

62

0

pT1

4680

4636

44

.17

b

.06b

pT

pT2

2045

2020

25

pT3/4

193

190

3

Unknown

40

40

00

.34b

.03b

Number of Positive Nodes None

3829

3789

40

22

16

1-3

2036

2015

21

13

8

4-9

593

586

7

7

0

10 or more

387

383

4

2

1

pNx

126

126

0

.90b

.47

Tumor Grade G1

1211

1205

6

1

5

G2

3111

3075

36

24

10

G3

2565

2536

29

18

10

84

83

1

1

0

1242

1192

50

44

3

Unknown

.13

.04

Receptor Status ER⫺/PgR⫺ ER⫺/PgR⫹

24

24

0

0

0

ER⫹/PgR⫺

771

766

5

0

5

ER⫹/PgR⫹

4934

4917

17

⬍ .0001

0

17

26

21

.0004

18

4

30

15

14

10

14

9

16

11

14

5

⬍ .0001

HER2/neu Not overexpressed

5683

5636

47

Overexpressed

1288

1263

25

Absent

4912

4865

47

Present

2059

2034

25

1797

1772

25

.10

PVI

.33

.23

Proliferative Fraction (Ki67) ⬍ 14%

96

14%-30%

2985

2958

27

ⱖ 30%

2189

2169

20

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.22

.20

Silvia Dellapasqua et al Table 1 Continued Characteristics

Total

Immunophenotypic Profilea

Histologic Subtype Ductal

Apocrine

P

Pure Apocrine

Apocrine-Like

20

5

P

CA15.3 ⬍ 16%

2949

2923

26

ⱖ 16%

2982

2940

42

22

19

Unknown

1040

1036

4

2

1

Luminal A

1689

1683

6

0

6

Luminal B

4040

4024

16

0

16

HER2

520

499

21

18

0

Triple negative

722

693

29

26

3

Conservative

5652

5598

54

32

20

Mastectomy

1319

1301

18

12

15

No

1060

1050

10

9

1

Eliot

1277

1258

19

External

4634

4591

43

.06

.07

Molecular Subtype

⬍ .0001

⬍ .0001

Type of Surgery

.19

.62

Radiation Therapy

.21

12

7

23

17

.21

Abbreviations: ⫺ ⫽ negative; ⫹ ⫽ positive; AR ⫽ androgen receptor; Eliot ⫽ electron intraoperative therapy; ER ⫽ estrogen receptor; PgR ⫽ progesterone receptor; pT ⫽ pathologic staging of T category primary tumor; PVI ⫽ peritumoral vascular invasion. a Immunophenotypic profile is undetermined for 3 patients; pure apocrine is defined as ER⫺/PgR⫺/AR⫹; apocrine-like is defined as ER⫹ or AR⫹. b Mantel-Haenszel test for trend.

Several subtypes of breast cancer exist, displaying a distinct morphology with a distinct prognostic and predictive profile.18 According to the latest edition of the World Health Organization classification, 17 distinct special types of breast cancer have been recognized, including apocrine breast cancers, which represent 8%-12% of all newly diagnosed breast cancers.19 Pure apocrine carcinomas are characterized by neoplastic cells with apocrine differentiation (defined by the presence of large cells with prominent eosinophilic, flocculent cytoplasm, with sharply defined cell borders, and with large nuclei containing prominent macronucleoli)20 and, irrespective of grade, by a characteristic steroid receptor expression profile, with negative (⫺) estrogen receptors (ER) and progesterone receptors (PgR) and positive (⫹) androgen receptors (AR).21 Recently published studies demonstrated that apocrine tumors are molecularly different from common luminal and basal-like subtypes thereby supporting a ‘molecular apocrine’ gene expression profile.8 Distinct expression of HER2 and epidermal growth factor receptor (EGFR) was observed in apocrine carcinomas. In fact, HER2 overexpressing apocrine carcinomas were mostly negative for EGFR protein, and a majority of HER2 negative cases (triple-negative apocrine carcinoma) overexpressed EGFR and could be classified as basal-like breast cancers. These findings might have significant therapeutic implications and might be associated with the patient’s outcome. Literature data indicate that immunohistochemically defined pure apocrine carcinomas (with an AR⫹/ER⫺/PR⫺ immunohistochemical profile) and apocrine-like carcinoma (luminal phenotype, with apocrine morphology without characteristic apocrine receptor pro-

file) display a prognosis similar to invasive ductal carcinoma not otherwise specified (NOS), with an outcome determined by the expression of biological features, such as HER2, EGFR, and steroid hormone receptors (ER, PgR, AR).22 Although apocrine carcinoma exhibits distinctive histopathologic and molecular features, the lack of standardized diagnostic criteria resulted in controversial and heterogeneous results in the literature in terms of its immunohistochemical profile and molecular classification. We therefore conducted a retrospective analysis on a series of invasive apocrine carcinomas (IAC) treated in our institution, exploring patterns of recurrence of IAC according to 2 immunohistochemically defined tumor subtypes—pure apocrine carcinoma (ER and PgR negative, and AR positive) and apocrine-like carcinoma (ER or PgR positive and AR negative)—as compared with pure invasive ductal carcinomas (IDC) NOS, to assess the prognostic role of distinct clinicopathologic and molecular features.

Patients and Methods Patients We extracted information from our institutional database, collecting information on all consecutive breast cancer patients who received surgery at the European Institute of Oncology. Between 1997 and 2005, 8801 patients with primary disease were identified. Patients with metastatic disease at the time of surgery, those with bilateral breast cancer, or with a history of previous cancer (other than skin cancer), and who received neoadjuvant chemotherapy were excluded. Histology was ductal in 6899 patients (78.4%), lobular in 875 (9.9%), mixed ductal and lobular in 341 (3.9%), cribriform in

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Apocrine Breast Cancer and Immunohistochemical Subtypes 251 (2.9%), mucinous in 147 (1.7%), tubular in 84 (1.0%), apocrine in 72 (0.8%), papillary in 45 (0.5%), tubule-lobular in 30 (0.3%), micropapillary in 20 (0.2%), metaplastic in 13 (0.1%), adenoid-cystic in 11 (0.1%), medullary in 8 (0.1%), and other in 5 (0.1%) patients. The analysis was restricted to 6971 women with either pure ductal NOS or apocrine breast tumor (either pure apocrine or apocrine-like carcinoma). Clinicopathologic data including age, tumor size, axillary lymph node status, tumor grade, receptor status, HER2 overexpression/ amplification, peritumoral vascular invasion (PVI), proliferative fraction (Ki-67), serum level of CA15-3, molecular subtype, type of surgery, radiotherapy, and type of adjuvant treatment (endocrine therapy alone, nonanthracycline-containing chemotherapy, or anthracycline-containing chemotherapy) were recorded in a database and included in the analysis.

Pathology and Immunohistochemistry All patients had pathologic evaluation performed at the European Institute of Oncology. The original tissue sections of all cases were retrieved and independently reviewed by 2 of the authors (GP and GM). All cases demonstrating distinct, invasive, neoplastic components other than apocrine histotypes and pure ductal NOS histotype were censored so that only patients with IAC and pure IDC, with or without an in situ component, were included in the current study. Tumor grade was independently assessed by the same 2 pathologists according to the criteria of Elston and Ellis,23 based on the combined assessment of tubule formation, nuclear grade, and mitotic activity, and, in case of disagreement, the case was reviewed again (together with GV) until a consensus was reached. Immunostaining for the localization of ER and PgR, AR, HER2 protein, and Ki-67 antigen was performed on consecutive tissue sections. The following primary antibodies were used: the monoclonal antibody (MAb) to ER (Dako, Glostrup, Denmark, at 1/100 dilution), the MAb to PgR (Dako, 1/800), the AR27 MAb to AR (Abcam, Cambridge, MA, 1:10 dilution), the MIB-1 MAb to the Ki-67 antigen (Immunotech, Marseille, France, 1/1200), and the CM1 polyclonal antiserum (Dako, 1/3200) to the HER2 protein.24 Only nuclear reactivity was taken into account for ER, PgR, AR, and Ki-67 antigen, whereas only an intense and complete membrane staining in ⬎10% of the tumor cells qualified for HER2 overexpression (3⫹). Fluorescence in situ hybridization assay (using the PathVysion HER2 DNA kit, Vysis-Abbott, Des Plaines, IL) was performed in cases with equivocal (2⫹) immunohistochemical results to identify cases with gene amplification (HER2 to chromosome 17 centromere ratio ⱖ2). The results for ER, PgR, AR, and Ki-67 were recorded as the percentage of immunoreactive cells observed among at least 2000 neoplastic cells. The value Ki-67 labeling index was divided into low (⬍14%) and high (ⱖ14%).25 The tumor was regarded as positive for ER and PgR if ⱖ1% of the cells showed nuclear staining, whereas a 10% cutoff was applied for AR staining.26,27 According to immunohistochemical evaluation we identified 4 subtypes: luminal A (ER and/or PgR positive, HER2⫺, Ki-67 low), luminal B (ER and/or PgR positive, HER2⫺, Ki-67 high; or ER and/or PgR positive, any Ki-67, HER2 overexpressed or amplified), HER2⫹ (HER2 overexpressed or amplified, ER and PgR absent), and triple negative (ER and PgR absent, HER2⫺).

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Statistical Analysis The Fisher exact test and the Mantel–Haenszel ␹2 test for trend were used to assess the association between categorical and ordinal variables, respectively. The primary end point was breast cancer-related disease-free survival (BRDFS). We selected BRDFS as primary end point because of the limited number of relapses and in particular deaths in a population characterized by an excellent prognosis. The secondary end point was overall survival (OS). BRDFS was defined as any event related to breast cancer (locoregional relapse, distant metastasis, contralateral breast cancer), or death, whichever occurred first. OS was determined as the time from surgery until the date of death (from any cause) or the date of last follow-up. Survival plots according to subtype were drawn using the Kaplan–Meier method. The log-rank test was used to assess the survival difference between strata. Multivariate Cox proportional hazard regression analysis was used to assess the independent prognostic significance of various clinical and histopathologic characteristics of the tumor on BRDFS or OS. Only those subtypes presented in 50 or more patients were selected. Factors included in multiple regression analyses included luminal subtype (A or B), tumor size (⬍ 2 or ⱖ 2 cm), nodal status (pN0 or pN⫹), PVI (absent or present), and Ki-67(⬍ 20% or ⱖ 20%). All analyses were performed with the SAS software, version 8.2 (Cary, NC). All tests were 2-sided and P values ⬍ .05 considered statistically significant.

Results Among the 8801 women with breast cancer who received surgery at the European Institute of Oncology from 1997 to 2005, 6899 had an IDC NOS and 72 had an IAC, for a total number of 6971 patients included in the present analysis. Median age was 52 years (range, 21-92). The median duration of follow-up was 5.6 years (range, 0-13.1) for breast cancer events (from surgery to last visit) and 6.3 years (range, 0-13.1) for overall survival (from surgery to last contact). Table 1 describes the clinicopathologic characteristics of the patients included in the analysis, stratifying apocrine patients into pure apocrine and apocrine-like. As expected, in the IDC group 71.2% of patients had an ER- and PgR-positive disease, as compared with 23.6% of the patients in the IAC group, whereas ER and PgR were negative in 69.4% of patients with IAC versus only 17.6% of patients with IDC (P ⬍ .0001). HER2 was overexpressed in 18.3% of patients with an IDC as compared with 34.7% of patients with an IAC (P ⫽ .0004). As for molecular subtypes, 24.3% of patients with an IDC and 8.3% of patients with an IAC were classified with a luminal A breast cancer, 58.3% and 22.2% with a luminal B, 7.2% and 29.1% with a HER2-positive disease, and 10% and 40.2% with a triple negative breast cancer, respectively (P ⬍ .0001). The majority of patients underwent conservative surgery and radiotherapy. The characteristics of 72 women with apocrine breast cancer according to immunophenotypic profile are shown in Table 2. In this group, 44 had a pure apocrine carcinoma (ER⫺/PgR⫺/AR⫹: 18 HER2⫹ and 26 triple negative) and 25 had an apocrine-like carcinoma (22 with ER⫹/PgR⫹/AR⫹: 6 luminal A and 16 luminal B; and 3 with ER⫺/PgR⫺/AR⫺, all triple negative) (P ⬍ .0001).

Silvia Dellapasqua et al Table 2 Characteristics of Women With Apocrine Breast Cancer According to Immunophenotypic Profile Immunophenotypic Profilea Molecular Subtype

Total

Undefined

Pure Apocrine ERⴚ/PgRⴚ/ARⴙ

Pa

Apocrine-Like

ERⴙ/ARⴚ

ERⴚ/ARⴚ

ER/ⴙARⴙ

Luminal A

6

0

0

—

0

6

Luminal B

16

0

0

—

0

16

HER2

21

3

18

—

0

0

Triple Negative

29

0

26

—

3

0

All Patients

72

3

44

0

3

22

⬍.0001

Positivity for ER and PgR defined as ⱖ 1%; positivity for AR defined as ⱖ 10%. Determination of AR is missing for 3 patients. Abbreviations: ⫺ ⫽ negative; ⫹ ⫽ positive; AR ⫽ androgen receptor; ER ⫽ estrogen receptor; PgR ⫽ progesterone receptor. a P value for pure apocrine versus apocrine ‘like’.

Table 3 Medical Treatment Proposed According to Histologic and Molecular Subtype Control (%)

Endocrine Therapy Alone (%)

Non Anthracycline-Containing Chemotherapy (%)

Anthracycline-Containing Chemotherapy (%)

Ductal

273 (4.0%)

3479 (50.4%)

1096 (15.9%)

2051 (29.7%)

Apocrine

11 (15.3%)

13 (18.1%)

25 (34.7%)

23 (31.9%)

Ductal

62 (3.7%)

1360 (80.8%)

91 (5.4%)

170 (10.1%)

Apocrine

1 (16.7%)

5 (83.3%)

—

—

80 (2.0%)

2118 (52.6%)

472 (11.7%)

1354 (33.7%)

—

8 (50.0%)

4 (25.0%)

4 (25.0%)

Ductal

67 (13.4%)

—

161 (32.3%)

271 (54.3%)

Apocrine

4 (19.1%)

—

8 (38.1%)

9 (72.9%)

Ductal

64 (9.2%)

1 (0.1%)

372 (53.7%)

256 (36.9%)

Apocrine

6 (20.7%)

—

13 (44.8%)

10 (34.5%)

P

Overall ⬍.0001

Luminal A

.30

Luminal B Ductal Apocrine

.38

HER2

.56

Triple Negative

Table 3 shows medical treatment proposed according to histologic and molecular subtype. Overall, endocrine therapy alone was prescribed in 50.4% of patients with an IDC and 18.1% of patients with an IAC, nonanthracycline-containing chemotherapy was prescribed to 15.9% of patients with IDC and 34.7% of patients with an IAC, and anthracycline-containing chemotherapy was prescribed to 29.7% of patients with IDC and 31.9% of patients with an IAC, and the difference was statistically significant (P ⬍ .0001). When molecular subtypes were separately taken into consideration, however, no treatment differences according to histologic subtype (either IDC or IAC) were found. Rates of locoregional relapse and distant metastasis are provided in Table 4. Multivariate Cox proportional hazard regression analysis was used to assess the independent effect of the histologic subtypes on disease-free survival (DFS) and OS, and the results are displayed in Figure 1. The diagnosis of pure apocrine carcinoma was correlated with a worse outcome in terms of DFS (hazard ratio [HR],

.23

1.7; 95% confidence interval [CI], 1.01-2.86; P ⫽ .0010), but not of OS, whereas IDC and apocrine-like breast cancers showed a similar outcome in terms of DFS and OS. Patients with either pure apocrine and apocrine-like breast cancers had an increased risk of contralateral breast cancer (HR, 4.12; 95% CI, 1.22-14; P ⫽ .02 for pure apocrine breast cancer; HR, 5.04; 95% CI, 1.24-21; P ⫽ .02 for apocrine-like breast cancer) (Table 5).

Discussion The reported prevalence of apocrine carcinoma ranges from 0.4% to 60% in different reports.28 This considerable variation seems to occur because of the absence of a uniform definition of apocrine carcinoma. We found a frequency of apocrine carcinoma of 0.8% as detected by the same team of pathologists, and using stringent criteria for the definition of pure apocrine or apocrine-like breast cancers. Among the 72 patients with an IAC, 44 had a pure apocrine carcinoma (ER⫺/PgR⫺/AR⫹: 18 HER2⫹ and 26 triple negative) and 25 had an apocrine-like carcinoma (22 with ER⫹/PgR⫹/AR⫹:

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Apocrine Breast Cancer and Immunohistochemical Subtypes Table 4 Number and Rate of Events Among Patients With Apocrine Breast Cancers Patients

Locoregional Relapse Events (Rate)

Distant Metastasis Events (Rate)

Contralateral Breast Cancer Events (Rate)

Disease-Free Survival Events (Rate)

Overall Survival Events (Rate)

Pure Ductal

6899

423 (1.1)

748 (1.8)

119 (0.3)

1237 (3.2)

649 (1.4)

All Apocrine

72

6 (1.8)

10 (2.7)

5 (1.3)

22 (6.4)

9 (2.1)

Pure Apocrine

44

5 (2.6)

7 (3.3)

3 (1.4)

15 (7.9)

6 (2.4)

Apocrine-Like

25

1 (0.7)

2 (1.3)

2 (1.3)

6 (4.3)

2 (1.2)

Rate of events is expressed per 100-year and calculated dividing the number of events by the number of patient-years at risk.

Figure 1 Disease Free Survival and Overall Survival According to Histologic Subtype

Disease free survival

Overall survival

100

100

80

80

Pure ductal Apocrine-like

60

60

Pure-apocrine

40

40

20

20 Log-rank P = 0.001

0 0

2

4

6

8

10

Years

0

2

4

6

8

10

Years

Number at risk 6899 6146 5376 3030 1284 227 44 36 26 8 3 0 25 23 18 10 5 1

6 luminal A and 16 luminal B; and 3 with ER⫺/PgR⫺/AR⫺, all triple negative). This compares well with the report by Vranic and colleagues: among patients with pure apocrine carcinoma 54% of patients had a HER2⫹ disease and 46% a triple negative breast carcinoma, with no luminal A or B tumors. In contrast, a large proportion of apocrine-like carcinomas belonged to the luminal group (76%), with 18% of triple negative breast carcinomas and 1 case only of HER2-overexpressing breast carcinoma. For these reasons, the authors conclude that strictly defined pure apocrine carcinomas are either HER2-overexpressing or triple negative breast carcinomas, whereas apocrine-like carcinomas predominantly belong to the luminal phenotype. Pure apocrine carcinomas show consistent overexpression of either EGFR or HER2/neu, which could have significant therapeutic implications.22 At the multivariate analysis, we found that the diagnosis of pure apocrine carcinoma was independently correlated with a worse outcome in terms of DFS (HR, 1.7; 95% CI, 1.01-2.86; P ⫽ .0010), whereas IDC and apocrine-like breast cancers showed a similar outcome in terms of both DFS and OS, indicating that pure apocrine carcinomas represent a distinct subtype of breast carcinomas. Because of the limited number of patients with IAC included in our

100

Log-rank P = 0.37

0

Number at risk Pure ductal Pure apocrine Apocrine-like

Apocrine-like Pure ductal Pure-apocrine

Clinical Breast Cancer April 2013

Pure ductal Pure apocrine Apocrine-like

6899 6754 6337 3828 1729 391 44 43 40 14 5 0 25 25 24 12 7 3

analysis, further investigations will be required to confirm our results. Patients with either pure apocrine and apocrine-like breast cancers had an increased risk of contralateral breast cancer (Table 5). If these data will be confirmed by other studies, a closer follow-up for the contralateral breast might be considered for patients with an IAC. Previously reported studies also showed that it is possible with microarray data to divide mammary tumor cells into 3 groups based on steroid receptor activity: luminal (ER⫹/AR⫹), basal (ER⫺/ AR⫺), and molecular apocrine (ER⫺/AR⫹). In addition, these studies reported a significant association between apocrine histology and molecular apocrine class.29 The present study provides morphologic and immunohistochemical validation to these gene expression findings. The combination of morphologic and immunohistochemical criteria are essential for the proper identification of pure apocrine carcinomas. We speculate that ‘molecular apocrine’ corresponds to immunohistochemically AR⫹/ ER⫺/PR⫺ tumors, and belong to pure apocrine carcinomas. We therefore highlight the need to determine ARs in case an invasive apocrine carcinoma is diagnosed, as the distinction between pure apocrine carcinoma (ER⫺/PgR⫺/AR⫹) and apocrine-like carcinoma has a prognostic implication.

Silvia Dellapasqua et al Table 5 Multivariate Analysis for Outcomes of Patients With Apocrine Versus Pure Ductal Breast Cancers Locoregional Relapse HR (95% CI)

Distant Metastasis HR (95% CI)

Contralateral Breast Cancer HR (95% CI)

Disease Free Survival HR (95% CI)

Overall Survival HR (95% CI)

Histologya 1.00

1.00

1.00

1.00

1.00

All apocrine

Ductal

1.44 (0.64-3.25)

1.22 (0.65-2.28)

4.30 (1.69-11.0)

1.67 (1.09-2.57)

0.95 (0.48-1.84)

Pure apocrine

1.90 (0.77-4.68)

1.25 (0.59-2.66)

4.12 (1.22-14.0)

1.70 (1.01-2.86)

0.81 (0.36-1.83)

Apocrine-like

0.76 (0.11-5.39)

0.83 (0.21-3.32)

5.04 (1.24-21.0)

1.53 (0.69-3.42)

1.03 (0.26-4.15)

Luminal A

1.00

1.00

1.00

1.00

1.00

Luminal B

1.46 (0.97-2.19)

1.69 (1.16-2.46)

0.92 (0.51-1.66)

1.37 (1.08-1.74)

1.52 (1.07-2.15)

HER2

2.78 (1.71-4.53)

2.70 (1.76-4.15)

1.26 (0.53-3.00)

2.34 (1.76-3.12)

3.30 (2.20-4.96)

Triple negative

1.88 (1.15-3.05)

2.02 (1.31-3.10)

1.91 (0.92-3.95)

1.84 (1.39-2.44)

3.54 (2.39-5.24)

⬍ 35

1.68 (1.17-2.42)

1.36 (1.05-1.77)

3.18 (1.78-5.67)

1.34 (1.08-1.67)

1.08 (0.80-1.47)

35-49

1.15 (0.93-1.42)

0.85 (0.72-1.00)

1.05 (0.70-1.57)

0.91 (0.80-1.03)

0.65 (0.54-0.79)

Molecular Subtype

Age (Years)

50-69

1.00

1.00

1.00

1.00

1.00

ⱖ 70

1.08 (0.75-1.56)

1.13 (0.86-1.47)

1.34 (0.67-2.65)

1.50 (1.24-1.81)

2.08 (1.66-2.60)

⬍ 2 cm

1.00

1.00

1.00

1.00

1.00

ⱖ 2 cm

1.45 (1.18-1.78)

2.12 (1.82-2.48)

0.87 (0.57-1.31)

1.79 (1.58-2.01)

2.05 (1.73-2.42)

Unknown

0.87 (0.25-2.72)

0.54 (0.13-2.16)

0.97 (0.13-7.06)

0.77 (0.34-1.73)

0.62 (0.15-2.50)

pN0

1.00

1.00

1.00

1.00

1.00

pN⫹

1.05 (0.84-1.31)

2.14 (1.79-2.56)

1.11 (0.74-1.67)

1.54 (1.35-1.76)

1.94 (1.61-2.34)

pNx

6.57 (3.98-10.8)

1.52 (0.90-2.55)

0.69 (0.09-5.15)

2.83 (2.03-3.95)

2.20 (1.49-3.21)

Absent

1.00

1.00

1.00

1.00

1.00

Present

1.44 (1.15-1.79)

1.51 (1.29-1.77)

1.18 (0.77-1.81)

1.36 (1.20-1.54)

1.44 (1.21-1.72)

Unknown

—

1.54 (0.49-4.80)

—

0.91 (0.29-2.82)

1.12 (0.36-3.51)

⬍ 20%

1.00

1.00

1.00

1.00

1.00

ⱖ 20%

1.98 (1.46-2.65)

2.40 (1.88-3.07)

1.18 (0.71-1.96)

1.86 (1.56-2.21)

1.65 (1.29-2.10)

Tumor Size

Nodal Status

PVI

Proliferative Fraction (Ki-67)

Hazard ratio and 95% CI are obtained from multivariate Cox proportional regression models. Abbreviation: PVI ⫽ peritumoral vascular invasion. a Risk estimates for ‘all apocrine’ and for apocrine subtypes are obtained from 2 separate multivariable models fitted with all other variables. The risk estimates for molecular subtype, age, tumor size, nodal status, PVI, and Ki-67 are derived from the model fitted with pure apocrine and apocrine ‘like’ categories.

The question raised by the present study is whether apocrine tumors would benefit from an androgen blockade. Previous studies failed to show any significant activity of antiandrogens in breast cancer.30 Future studies of endocrine therapy should take into account the role of AR in pure IAC.31 Currently, several studies are investigating AR driven transcription in molecular apocrine breast cancer. Studies in cell line models show that AR binds and regulates ER cis-regulatory elements in molecularly defined apocrine tumors, resulting in a transcriptional program reminiscent of ER-mediated transcription in luminal breast cancers. The loss of ER expression might result in a shift from ER⫺

to AR–mediated transcription, which would result in similar genes being expressed from common cis-regulatory domains, but growth would occur in a manner that is refractory to traditional breast cancer therapies. The lack of clinical benefit from ER antagonists, such as tamoxifen and aromatase inhibitors, is reflected in the poor clinical outcome of molecular apocrine tumors, when compared with luminal breast cancers.32

Conclusion In conclusion, pure apocrine carcinoma has a worse DFS as compared with apocrine-like and infiltrating ductal carcinoma. When-

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Apocrine Breast Cancer and Immunohistochemical Subtypes ever an infiltrating apocrine carcinoma is diagnosed, ARs should be determined in the breast cancer specimen, for this might have an important prognostic and—possibly, in the future—therapeutic implication.

Clinical Practice Points ● ●

●

Data on prognosis of IAC are inconsistent in the literature, possibly because of a heterogeneous classification of these tumors. We explored patterns of recurrence of 2 different immunohistochemically defined subtypes of IAC, pure apocrine carcinoma and apocrine-like carcinoma, comparing them with IDC. We found that pure apocrine carcinoma represents a distinct subtype of breast cancer with a significantly worse DFS as compared with IDC, whereas IDC and apocrine-like breast cancers showed a similar outcome in terms of DFS and OS. Patients with pure apocrine carcinoma had also an increased risk in contralateral breast cancer. Pure apocrine carcinoma is characterized by AR expression. Based on our results, AR determination might have an important prognostic implication and AR-targeted therapy should be further explored in IAC.

Disclosure All authors have no conflicts of interest.

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