SULT1A1 gene deletion in BRCA2-associated male breast cancer: a link between genes and environmental exposures?

SULT1A1, a member of sulfotransferase superfamily, is a drug and hormone metabolizing enzyme involved in the metabolism of a variety of potential mammary carcinogens of endogenous and exogenous origin. Interestingly, the metabolic activity of SULT1A1 can be affected by variations in gene copy number. Male Breast Cancer (MBC) is a rare disease and less investigated disease compared to female BC (FBC). As in FBC, the concurrent effects of genetic risk factors, particularly BRCA2 mutations, increased exposure to estrogens and environmental carcinogens play a relevant role in MBC. By quantitative real-time PCR with TaqMan probes, we investigated the presence of SULT1A1 gene copy number variations (CNVs) in a series of 72 MBCs. SULT1A1 gene deletion was observed in 10 of the 72 MBCs (13.9%). In a multivariate analysis association between BRCA2 mutation and SULT1A1 gene deletion emerged (p = 0.0005). Based on the evidence that the level of SULT1A1 enzyme activity is correlated with CNV, our data suggest that in male breast tumors SULT1A1 activity may be decreased. Thus, it can be hypothesized that in a proportion of MBCs, particularly in BRCA2-associated MBCs, the level of estrogens and environmental carcinogens exposure might be increased suggesting a link between gene and environmental exposure in the pathogenesis of MBC.

SULT1A1, a member of sulfotransferase superfamily, is a drug and hormone metabolizing enzyme involved in the metabolism of a variety of potential mammary carcinogens of endogenous and exogenous origin, including oestrogens and polycyclic aromatic hydrocarbons (PAHs) 1.

Gene copy number variations (CNVs) are increasingly recognized to play a relevant role in the expression of drug metabolizing genes and in their respective enzymatic activities. In particular, the metabolic activity of SULT1A1 can be affected by variations in gene copy number 2.

Male breast cancer (MBC) is a rare disease, compared with female BC. The concurrent effects of genetic risk factors, particularly BRCA2 mutations, increased exposure to oestrogens and environmental carcinogens play a relevant role in MBC 3. MBC is unaffected by the strong confounding effects of high disease frequency and of reproduction-related variables, thus, the complex effects of genetic, hormonal and environmental factors, involved in the pathogenesis of BC in both genders, can be better investigated in MBC.

On the basis of SULT1A1 biochemical properties, we investigated the presence of SULT1A1 CNVs in a series of 72 MBCs characterized for relevant clinical-pathologic features, including BRCA1/2 mutation status 4. SULT1A1 CNVs were analysed by quantitative real-time PCR with TaqMan probes (Life Technologies, Carlsbad, CA, USA) comparing DNAs from tumour and blood from each MBCs included in the study. Normal breast tissue was used as calibrator sample. The fold change in studied gene copy number, normalized to endogenous control, was calculated using Relative Quantity (RQ) = 2−ΔΔCt.

SULT1A1 gene copy number differences were found to occur in tumour compared with matched blood samples in 10 of the 72 MBCs (13.9%). In particular, SULT1A1 gene deletion (RQ = 0.5) was observed indicating the presence of a single copy of SULT1A1 gene in the 10 tumour samples compared with two copies (RQ = 1) detected in the corresponding blood samples. The results of blood and normal breast tissue paired samples were comparable in each patient.

As shown in Table 1, statistically significant association emerged between SULT1A1 gene deletion and BRCA2 mutations (P < 0.0001) and ER-negative status (P = 0.03). However, in a multivariate analysis only the association for BRCA2 status persisted (P = 0.0005).

Table 1

Distribution of 72 MBC cases according to SULT1A1 gene deletion and clinical-pathologic features

SULT1A1
Parameter*	Deletion (%)	No deletion (%)	P value†
Family history of breast/ovarian cancer
Negative	4 (8.2)	45 (91.8)	0.06
Positive	6 (27.3)	16 (72.7)
Personal history of cancer
Negative	7 (11.7)	53 (88.3)	0.18
Positive	3 (27.3)	8 (72.7)
BRCA1 status
BRCA1 wt	10 (14.5)	59 (85.5)
BRCA1 mutation	0 (0)	2 (100.0)	1.0
BRCA2 status
BRCA2 wt	4 (6.3)	60 (93.7)	<0.0001
BRCA2 mutation	6 (85.7)	1 (14.3)
ER
Negative	4 (40)	6 (60.0)	0.033
Positive	6 (9.7)	56 (90.3)
PR
Negative	4 (25.0)	12 (75.0)	0.12
Positive	6 (10.7)	50 (89.3)
HER2
Negative	5 (9.4)	48 (90.6)	0.12
Positive	4 (22.2)	14 (77.8)
Ki-67
Low	4 (10.0)	36 (90.0)	0.2
High	5 (16.1)	26 (83.9)
Histological grade
G1/G2	3 (6.8)	41 (93.2)	0.06
G3	6 (25.0)	18 (75.0)
Lymph node status
Negative	1 (3.9)	25 (96.2)	0.35
Positive	4 (14.3)	24 (85.7)
Total	10 (13.9)	62 (86.1)

Some data for each parameter are not available.

From Fisher exact test.

This association was not evident in a multivariate analysis.

To date, there are no data on CNVs of SULT1A1 gene in BC. We found that a quite relevant proportion of MBCs (about 14%) showed SULT1A1 gene deletion and, interestingly, that the deletion was significantly found in BRCA2-associated tumours. Based on the evidence that the level of SULT1A1 enzyme activity is correlated with CNV 2, our data suggest that in male breast tumours SULT1A1 activity may be decreased.

It has been reported that oestrogen sulfotransferases are frequently decreased in breast carcinomas and this may result in an increased exposure of mammary tissue to oestrogens 5. Very recently, SULT1A1 has been shown to play an important role in the detoxication of PAHs in lung cells 6. Thus, based on our results, it can be suggested that in a proportion of MBCs, particularly in BRCA2-associated MBCs, the level of oestrogens and environmental carcinogens exposure might be increased. This could be particular relevant considering the important role of oestrogens in MBC pathogenesis and the molecular crosstalk between oestrogens and BRCA2 gene 7. Intriguingly, we have previously shown an interaction between BRCA carrier status and occupational exposure to chemicals, such as PAHs, in MBC patients 8. Thus, our present results may help to clarify possible pathogenetic mechanisms underlying this interaction.

Overall, our data suggest that MBCs, particularly BRCA2-associated MBCs, may be characterized by low SULT1A1A enzymatic activity thus suggesting a link between gene and environmental exposure and opening interesting questions on clinical settings.