Phospho-Akt and PTEN in breast cancer

Table 2. Association between Phospho-Akt
and PTEN expression

mor size and lymph node metastasis. There wasno significant association between Phospho-Akt
expression and loss of PTEN expression, althougha tendency was observed (Table 2, P = 0.08).

Positive

Negative

Phospho-Akt

91

120

PTEN

119

102

P value
0.08

Disease-free survival and over-all survival
rates
Patients with Phospho-Akt-positive tumor showeda significantly inferior disease-free survival
rate compared to those with a negative tumor(Fig. 3A). Figure 3B shows the over-all survival
curves for patients with breast cancer stratiﬁed by
Phospho-Akt expression. Patients with PhosphoAkt-positive tumors showed signiﬁcantly shorter

over-all survivals than those with Phospho-Aktnegative tumors. Furthermore, patients with
PTEN-positive expression had signiﬁcantly better
disease-free survival rate than those with PTENnegative expression (Fig. 4A). There was a significant difference in over-all survival between
patients with PTEN-positive and -negative expres-Fig. 3. Disease-free survival curves (A) and over-all survival curves (B) of breast cancer patients. Patients with Phospho-Akt positive tumors are signiﬁcantly inferior to those with Phospho-Akt negative tumors in both disease-freesurvival and over-all survival. mo, month. [ ], number of subjects.

Fig. 4. Disease-free survival curves (A) and survival curves (B) of breast cancer patients. Patients with PTEN positive tumors show higher results than those with PTEN negative tumors in both disease-free survival and over all survival. mo, month. [ ], number of subjects.

23

O. Yamamoto et al.

Fig. 5. Disease-free survival curves (A) and over-all survival curves (B) of breast cancer patients. The disease-freesurvival curve and over-all survival curve of patients who had tumors in Group B were signiﬁcantly lower than thoseof patients who had tumors in Group C. mo, month. [ ], number of subjects; +, positive; –, negative.

sions (Fig. 4B). For further analysis of survival
in relation to Phospho-Akt and PTEN expression,
patients were classiﬁed into the following groups:
Group A, positive expression in both PhosphoAkt and PTEN (Fig. 5A: n = 38, Fig. 5B: n = 44);
Group B, positive in Phospho-Akt and negative in
PTEN (Fig. 5A: n = 38, Fig. 5B: n = 47); GroupC, negative in Phospho-Akt and positive in PTEN
(Fig. 5A: n = 73, Fig. 5B: n = 75); and Group D,
negative in both Phospho-Akt and PTEN (Fig.
5A: n = 51, Fig. 5B: n = 55). Disease-free survival and over-all survival of patients in eachgroup are shown in Fig. 5. For both disease-freesurvival and over-all survival, patients in Group B
had worse results than those in the other groups.
Both disease-free survival and over-all survival ofpatients in Group C were signiﬁcantly better thanthose in the other groups. Additionally, there wasno signiﬁcant association between Groups A and
D in disease-free survival (P = 0.9176) and overall survival time (P = 0.8144).

The analysis revealed that expression of PhosphoAkt and tumor size were the independent factors.

Multivariate analysis

Age
Size (2 cm ≥/2 cm <)Lymph-node metastasis
Phospho-AKT
PTEN

Discussion
Considerable evidence indicates that PI3-kinase
regulated signaling pathways play important roles
in a variety of cellular processes (Khwaja et al.,1998) and that the protein kinase, Akt, and PTEN
are important mediators of these effects (Crosset al., 1995; Gingras et al., 1998; Hajduch et al.,
1998; Van Weeren et al., 1998). The role of PI3kinase in the suppression of apoptosis and theability of Akt to directly phosphorylate key mediators of the apoptotic response provide strong
Table 3. Multivariate analysis by the Cox proportion hazard model for disease-free survival
in 200 patients with breast cancer
Hazardratio

To determine which of the many covariates in thefactors listed in Table 3 were important prognostic factors of disease-free survival, a multivariate
analysis with a Cox regression analysis was done.

CI, conﬁdence interval.

24

95%
CI

0.978 0.951–1.007
0.243 0.086–0.683
0.861 0.360–2.062
0.368 0.154–0.877
0.588 0.255–1.356

P
value
0.140
0.007
0.737
0.024
0.212

Phospho-Akt and PTEN in breast cancer

cancer. Patients with PTEN positive breast cancer survived signiﬁcantly longer than those witha PTEN negative tumor. Furthermore, PhosphoAkt expression and loss of PTEN expression were
frequently observed in patients with advanced
breast cancer. Patients with Phospho-Akt-negative and PTEN-positive tumors showed the best
prognoses, whereas those with Phospho-Akt positive and PTEN negative tumors showed the worst.
Therefore, monitoring the status of Phosph-Akt
and PTEN protein expression might predict survival in patients with breast cancer.
The Akt phosphorylation status in eachcarcinoma case can monitor aspects of malignancies such as cell proliferation rate, resistance tochemotherapy and irradiation, invasion and metastasis, and patient prognosis (Brognard et al.,
2001; Clark et al., 2002; Itoh et al., 2002; Semba
et al., 2002). At present, no speciﬁc inhibitor for
Akt is available, though the PI3-kinase inhibitor,
LY294002, is widely used in laboratories. It canbe speculated that LY294002 inhibits some otherdownstream effectors of PI3-kinase in addition
to Akt; the MAPK cascade and small G protein,
Rac/Cdc42, are reported to be downstream of Akt(Cross et al., 1995). Izuishi et al. (2000) reported
that LY294002 administration with tumor embolization may be a new therapeutic strategy forpatients with pancreatic cancer. These findings
suggest the possibility of treating human malignancy using the PI3-kinase inhibitor. Our results
indicate that activation of the PI3-kinase pathway
is a common occurrence in human breast cancers,
especially in more advanced stages. Thus, regulating the PI3-kinase pathway could be of beneﬁt
and may increase the effectiveness of therapies forpatients with breast cancer.
In conclusion, Phospho-Akt/PTEN expression status could be a deﬁnitive prognostic factor
in clinical breast cancer. Further studies concerning the regulation of the PI3-kinase pathway inbreast cancer are urgently required.

circumstantial evidence for the importance of the
PI3-kinase-Akt pathway in the aberrant behaviorof cancer cells. The tumor suppressor PTEN acts
as a lipid phosphatase, regulates the PI3-kinase/Akt-signaling pathway, and modulates cell cycle
progression and cell survival. Recent studies haveshown that the most critical tumor-cell survival
pathways are those mediated by PI3-kinase (Chanet al., 1999; Ling-Ping et al., 1999).
In the current study, Phospho-Akt was observed in cytoplasm and nucleus of tumor cells.
Staining patterns were consistent with reports that
activated Akt could translocate to the nucleus inectopically Akt-overexpressing cells (Andjelkovic
et al., 1997; Meier et al., 1997). As reported previously, the PI3-kinase pathway is an essential
survival signaling pathway for various humancancers, including carcinomas of the colon, prostate, ovary, pancreas and lung (Maulik et al.,
2002; Mei Sun et al., 2001; Roy et al., 2002).
It is known that patients with both estrogen
receptor (ER)- and progesterone receptor (PgR)negative tumors experienced signiﬁcantly shorter
disease-free survival compared to those who’s tumors were positive in either or both. The relationship between a dysregulated PI3-kinase pathway
and reduced ER/PgR expression in human breast
cancers has been reported previously (Depowski
et al., 2001; Shi et al., 2003). Kappes et al. (2001)
reported that there was a significant correlation
between PI3-kinase pathway abnormalities andthe hormone receptors. However, there was noapparent correlation between these factors in ourstudy (data not shown), though the precise mechanism behind this observation is not entirely clear.
It has been noted by others that increased AktmRNA correlates with ER-negative breast tumors(Nakatani et al., 1999) and increased ER α activity, which results in tamoxifen resistance (Campbell et al., 2001).
It is reported that a loss of expression of the
PTEN gene protein product is associated with apoor outcome in breast cancer (Depowski et al.,2001). In the current study, PTEN expression inversely correlated with the progression of breast25

O. Yamamoto et al.

Acknowledgments: We would like to thank Dr. Y.
Yamaguchi and Dr. H. Kudou of Tottori Red Cross
Hospital for giving us permission to use their data frompatients who they had operated on for breast cancer

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Received December 26, 2005; accepted January 4, 2006
Corresponding author: Osamu Yamamoto27