				Using the search form

Advances in treating early breast cancer

A new, alternative approach to breast conservation treatment involves accelerated partial breast irradiation utilizing a high-dose rate balloon catheter system.

Katherine Y. Hanley, PA-C, MA; Alan Beckman, MD; Marta Hayne, MD

The authors work at Radiation Oncology of Lexington and Central Baptist Hospital, Lexington, Ky. They have indicated no relationships to disclose relating to the content of this article.

If you prefer to view this article in PDF form, click here.

For an explanation of competencies, click here.

Breast cancer continues to occupy a prominent role in the public consciousness, and the media heighten that interest with a regular influx of new information from multiple sources, often conflicting and confusing. Breast cancer touches most health care providers in some way, whether personally or professionally; many will treat patients with the disease. With the overwhelming information available, all providers would benefit from a basic understanding of the rationale of current treatment approaches for early breast cancer, as well as of the promising new options in radiotherapy.

Incidence and prevalence

The American Cancer Society (ACS) estimates that in 2005, approximately 211,240 new cases of invasive breast cancer will be diagnosed in the United States, and 40,410 women will die from the disease.¹ At 32%, breast cancer is the most frequently diagnosed cancer in women, and a woman’s lifetime risk of developing breast cancer is now 1 in 7, whereas it was 1 in 11 in 1975.¹ The risk of developing breast cancer increases with age; the majority of new cases occur in women older than 50 years. In total, 1 in 33 women will die of breast cancer; it is the second leading cause of cancer deaths in women, after lung cancer and before colon cancer.¹ However, between 1990 and 2000, breast cancer mortality declined 2.3% annually, and today’s 5-year survival rates for breast cancer can be higher than 97% in women with early-stage disease. Fortunately, more than 60% of women with breast cancer now receive a diagnosis of early-stage disease.^1,2

Current screening guidelines for breast cancer

While ongoing technological advances in breast imaging do have an impact on breast cancer screening and follow-up recommendations in selected patients, the ACS³ and National Cancer Institute⁴ (NCI) currently continue to recommend the following general screening guidelines:

Women should have routine mammography every 1 to 2 years starting at age 40 years.
Routine clinical breast examinations should be performed as part of routine health screenings, beginning in the third decade.
Women should know how their breasts normally feel and report any change to their health care providers. Breast self-examination is an option for women starting in their 20s.
Women at increased risk of breast cancer should discuss with their medical provider the benefits and limitations of starting mammography screening earlier; having additional tests, such as breast ultrasonography and MRI; or having more frequent examinations.

Quantifying risk—the Breast Cancer Risk Assessment Tool

The NCI’s Breast Cancer Risk Assessment Tool (BCRAT), a modified Gail Model, is a computer-based program, available to anyone, that calculates a woman’s relative risk for the development of invasive breast cancer over a 5-year period and over her lifetime to age 90 years and compares this to same-age women of average risk. Only about 20% of diagnosed breast cancer cases can be accounted for by standard risk factors: age, age at menarche, age at first live birth, number of first-degree relatives (mother, sisters, and/or daughters) with breast cancer, number of previous breast biopsies (whatever the findings), at least one biopsy finding of atypical hyperplasia, and history of lobular carcinoma in situ (LCIS) or ductal carcinoma in situ (DCIS).

The program will underestimate the risk for a woman with a previous diagnosis of breast cancer and does not take into account inherited genetic mutations (BRCA1 or BRCA2) for breast cancer. The projections assume that the woman is receiving regular clinical breast examinations and undergoing routine screening mammography. Other risk factors, such as age at menopause, dense breast tissue on mammogram, use of oral contraceptives or hormone replacement therapy, high-fat diet, alcohol use, physical inactivity, obesity, or environmental exposures, were not included; evidence is either inconclusive or contribution to overall risk from these factors cannot be calculated. The BCRAT is available at http://bcra.nci.nih.gov/brc.

Breast cancer prevention—the STAR trial

The National Surgical Adjuvant Breast and Bowel Project (NSABP) Study of Tamoxifen and Raloxifene (STAR) accrued more than 19,000 postmenopausal women in Canada, the United States, and Puerto Rico over 5 years and formally closed to enrollment in 2004. Its purpose is to compare tamoxifen and raloxifene for the prevention of invasive breast cancer in postmenopausal women at high risk (greater than 1.66% by BCRAT or a history of LCIS). The rationale for the STAR is based on data from the Breast Cancer Prevention Trial, which is the backbone of tamoxifen data, and the MORE (Multiple Outcomes for Raloxifene) trial. While the STAR has stopped accruing patients, women can still discuss their relative risks of breast cancer and the risks and benefits of the preventive use of tamoxifen or raloxifene with their health care provider. The Web site for the STAR is www.nsabp.pitt.edu/STAR/Index.html.

Early breast cancer: Surgical approaches

The trend in the surgical management of early-stage breast cancer (DCIS stages I and II) has been to progress toward less extensive approaches to improve morbidity and cosmesis without compromising patient outcomes—specifically, locoregional control, disease-free survival, and overall survival. Current surgical procedures include traditional modified radical mastectomy and breast conservation treatment (BCT), which includes lumpectomy followed by adjuvant radiation therapy. Approaches to the axilla include sentinel lymph node dissection versus traditional axillary lymph node dissection.

Meta-analyses of multiple large-scale clinical trials of mastectomy or breast conserving surgery with or without radiation concluded that the rate of local recurrence was three times lower with BCT than with lumpectomy alone. Local recurrence rates for BCT were comparable to those for mastectomy, but there were no significant differences in the three groups in disease-free survival, distant-disease-free survival, or overall survival.^5,6 Based on these data, the 1990 NCI/NIH Consensus Development Conference on the treatment of early-stage breast cancer stated, “BCT is an appropriate method of primary therapy for the majority of women with stage I–II breast cancer and is preferable because it provides survival equivalent to total mastectomy and axillary dissection while preserving the breast.”⁷

Separate clinical trials have demonstrated similar findings in DCIS.^8,9 Chemotherapy, including therapy with tamoxifen, has not been shown to reduce local recurrence after lumpectomy for invasive cancer or DCIS in premenopausal or postmenopausal women, except in those patients who also receive radiation.^9-12 There is an ongoing Radiation Therapy Oncology Group (RTOG) trial to assess the efficacy of lumpectomy without adjuvant radiotherapy in low- to intermediate-grade DCIS only.¹³

Breast irradiation for older women

Until recently, there had been no clearly defined subset of patients who would not benefit from the addition of radiotherapy in BCT. However, two recent studies suggest that women older than 70 years with early-stage, node-negative, estrogen-receptor-positive breast cancer have minimal absolute improvement in local recurrence risk at a median follow-up of 5 years with tamoxifen plus radiotherapy (4%) versus tamoxifen alone (1%), with no difference in disease-free survival or overall survival.^12,14

Sentinel lymph node dissection for axillary lymph node staging

Lymph node status has implications for breast cancer staging and prognosis, selection of adjuvant treatment, regional control, and the possibility of improved disease-free and overall survival. Approximately 75% of patients with operable breast cancer have negative nodes upon dissection. The rationale behind sentinel lymph node dissection is that metastasis to regional lymph nodes follows an orderly pattern within the lymphatic system and that the primary or sentinel node is the first to contain metastases. Biopsy of this node should accurately predict axillary involvement. Less extensive axillary dissection is preferable in terms of quality of life and morbidity; less invasive axillary surgery generally translates into a decreased risk of pain, numbness, and arm swelling and into improved arm mobility. Large multicenter trials have established the accuracy of sentinel node detection and its predictive value as to axillary lymph node status.^15,16 Ongoing clinical trials are also comparing sentinel lymph node dissection alone to sentinel lymph node dissection plus axillary lymph node dissection for long-term locoregional control, disease-free survival, overall survival, and comparative morbidities. These studies will also examine the predictive value and optimal histologic and pathologic techniques of sentinel node evaluation.^17,18 No trials have addressed the possible role of regional lymph node irradiation in the setting of negative sentinel lymph node dissection. One must rely on extrapolations from postmastectomy data and comparative local recurrence rates following BCT with axillary lymph node dissection for a given lesion.

Of note, risk factors for local recurrence versus distant metastases vary somewhat in the setting of BCT. EIC—which is extensive intraductal carcinoma, defined as intraductal carcinoma comprising more than 25% of the area encompassed by the infiltrating tumor, intraductal cancer in the surrounding breast tissue, or predominantly intraductal cancer with one or more areas of focal invasion—is a predictor of local recurrence risk, while tumor size, node status, and histologic grade are more strongly associated with risk of distant metastasis.^19,20 Young age, peritumoral lymph-vascular invasion, and involvement of the excision margin are risk factors for both types of recurrence risk.^19,20

Contraindications to breast conservation treatment

There are actually very few contraindications to BCT. For most women, the choice of BCT versus mastectomy can be a matter of personal preference.

Absolute contraindications include pregnancy (first or second trimester), diffuse suspicious calcifications, previous radiation to the region, and inability to achieve negative margins (particularly with EIC). Relative contraindications include two or more gross tumors (multicentric disease) in different quadrants, tumor greater than 5 cm initially or after neoadjuvant chemotherapy, large tumor-breast ratio for cosmesis, and collagen vascular disease.

Standard whole breast irradiation in BCT

Patients typically have many fears in anticipating the radiation experience. Fortunately for patients having BCT, the treatment course is usually well tolerated and produces limited side effects. Of note, if systemic chemotherapy is indicated, it will usually be completed before the initiation of radiotherapy because there is no negative impact on local control or disease-free survival and the chemotherapy may benefit overall survival. Doses of 45 to 50 Gray (Gy) are typically given to the whole breast, in daily, Monday-to-Friday fractions of 180 to 200 centiGray (cGy), over a 5-week period, followed by a tumor bed boost of an additional 10 to 16 Gy over 1 to 2 weeks. Pathologic nodal status will determine whether regional nodal groups also require concomitant adjuvant radiotherapy in doses that are similar to those given to the whole breast.

In discussing treatment with the patient, the clinician should explain that treatments are typically given on a linear accelerator and that there will be a treatment planning session or simulation of about an hour before the start, which will define the treatment fields and mark the skin. Total daily treatment time usually averages 15 to 20 minutes. The treatments are not painful, and the radiation cannot be seen or felt. Radiotherapy is a local treatment that works only where the beams are pointed. Breast irradiation will not cause hair loss of the scalp, nausea, or lowered immunity, and it should not harm the heart, lungs, or spinal cord. Reassure the patient that she will not be radioactive, does not need to monitor physical proximity to others, and need not take special precautions with clothes, urine, or stool.

Typical side effects include skin reactions ranging from mild redness, dryness, and itching to less frequent moist desquamation, ulceration, and infection (see Figures 1, 2, and 3). All usually heal well after treatment. The patient may also experience occasional mild shooting pains in the treated breast and axilla, as well as some fatigue, which is not usually related to low blood counts. There is a low but long-term risk of scarring or fibrosis (eg, fat necrosis) of the treated breast and tumor bed, alteration of breast symmetry, and hyperpigmentation, telangiectasias, or altered skin texture. Adding radiotherapy after surgery increases the risk of lymphedema—especially following axillary lymph node dissection (18%) as opposed to sentinel lymph node dissection (10%)—and decreased range of motion of the ipsilateral upper extremity.^21,22 Other potential side effects, such as neuropathy, plexopathy, radiation pneumonitis, rib fracture, cardiac events and mortality in women with left breast cancer, and risk of secondary primary malignancies, all average less than 1%. There is no correlation to risk of contralateral breast cancer.^23,24

In spite of the data and excellent tolerability of treatment, more than 40% of women with early-stage breast cancer still opt for mastectomy, despite long-term local recurrence and survival rates comparable with those for BCT.^25,26 Up to 25% of women who undergo lumpectomy do not proceed to radiation therapy.²⁶

New treatment: Partial breast accelerated radiotherapy

Reviews of local recurrence data show that 80% to 90% of breast cancer recurrences after BCT occur at or near the tumor bed. Radiotherapy of the whole breast does not further decrease risk of failures in the breast outside of the lumpectomy area (less than 4% regardless of radiotherapy).^27-31 Therefore, intensifying radiotherapy to the tissue at greatest risk for subclinical disease may further decrease local recurrence risk while potentially reducing the acute and chronic toxicities of radiotherapy. Cosmetic outcomes and quality of life may improve because skin and breast parenchymal doses are lower. This is especially true for women with large breasts, who typically experience more significant skin reactions. Because partial breast irradiation requires a much shorter treatment course—twice-daily treatments for 5 days—it may also affect the documented underutilization of BCT by decreasing patient time commitment and inconvenience.

There is variability in patient selection criteria for partial breast irradiation; however, selection criteria generally accepted by the American Brachytherapy Society (ABS)²⁸ and the American Society of Breast Surgeons (ASBS)³² include the following:

Age 45 years or older (ABS) or 50 years or older (ASBS)
Tumor size 3 cm or less (ABS) or 2 cm or less (ASBS)
Surgical margins negative by 5 mm or more (greater than 2 mm, ASBS; negative microscopically, ABS)
Negative nodes (unless on formal research protocol)
Lobular histology excluded
EIC excluded; no evident multifocal/multicentric disease
DCIS with adequate surgical margins.

Traditional low-dose rate/high-dose rate breast brachytherapy

Brachytherapy is the use of radioactive implants placed in direct contact with the site of disease. Multicenter studies of partial breast irradiation utilizing traditional low-dose rate and/or high-dose rate brachytherapy with more than 2-year follow-up data have shown local recurrence rates to be consistently less than 5%, with good to excellent cosmetic results.^27-31 However, there are multiple barriers to the widespread use of brachytherapy, including the time involved in the procedure, the technical expertise required to perform it, difficulties in ensuring consistent dose delivery and uniform target coverage, risk of pneumothorax, and patient acceptance. Thus, partial breast irradiation is not standard therapy at this time.

MammoSite^® high-dose rate partial breast irradiation

With MammoSite high-dose rate brachytherapy, newer forms of image guidance such as ultrasonography and CT 3D dosimetry can be utilized for technique and planning, improving target coverage, homogeneity, reproducibility, and overall outcomes. Techniques and training are simplified and standardized for surgeons and radiation oncologists in order to maximize utilization and to minimize morbidity and late radiation complications. Ideally, this will increase availability and reduce cost of care for appropriate patients, without compromising results.

After patient criteria are reviewed and the patient selects MammoSite partial breast irradiation, the MammoSite flexible balloon catheter can be placed through the lumpectomy incision or through a separate incision, either at the time of surgery or later with ultrasound guidance (see Figure 4, and the image at the top of the page). Surgeons may choose to place the catheter after surgery in order to review margin of resection, nodal status, and other pathologic considerations such as EIC. However, if use of the MammoSite system is being considered, the lumpectomy cavity should not be clipped, as this may cause balloon puncture.

Based on the size of the lumpectomy cavity, the MammoSite catheter balloon is then filled with a specified volume of saline solution. The catheter partially extrudes from the breast and is loosely anchored with gauze dressings, not sutured in place. Antibiotic prophylaxis is typically given at the time of implantation. The catheter is fairly uncomfortable but usually well tolerated.

MammoSite key parameters The radiation oncologist must evaluate for balloon-to-skin distance, tissue conformity around the balloon, and balloon symmetry with the aid of CT in order to proceed with treatment; not all potential candidates will meet the accepted criteria for actual treatment delivery. The overall catheter pull rate as noted in the MammoSite Patient Registry is about 11%. Technical criteria are also reevaluated daily during treatment with repeat CT or ultrasound measurements. Radiation dose delivery is 34 Gy in 10 twice-daily fractions at least 6 hours apart, or a boost of 5 Gy in 2 twice-daily fractions, to be followed by whole breast irradiation. Boost treatment only with MammoSite is an option that may also gain acceptance as part of BCT. The radiation staff generally deflates and removes the catheter after the last treatment; at our institution, we apply a small amount of EMLA Cream beforehand to minimize the associated discomfort.

MammoSite side effects and cosmetic outcomes The most commonly encountered acute side effects of the MammoSite procedure are erythema at the catheter entrance site and surrounding skin, serous drainage at the catheter insertion site, pain and discomfort of the treated breast, ecchymosis, and mild edema. Less common side effects include seroma formation, infection or mastitis, skin discoloration, bloody drainage, or moist desquamation.

Educating patients about proper dressing care is of paramount importance to prevent development of infection, which has been seen in 2% to 6% of patients.^31,33 The catheter manufacturer provides patient instruction materials, including detailed dressing change instructions. The radiation staff sees the patient twice daily during treatment and changes the dressing on those days. However, there is usually a short delay between catheter placement and the initiation of treatment, and at the time of catheter placement or before, the patient and family member(s) must be given supplies and educated as to when to change the dressing and the proper technique to use.

Small-scale, 3-year follow-up data show good to excellent cosmetic outcomes in 86% of patients, comparable to those reported with conventional radiotherapy.³¹ Toxicity at 3 years remains minimal.³¹ Patients and providers can obtain more information by accessing the Web site www.MammoSite.com.

Final note on partial breast irradiation

An active RTOG/NSABP multicenter phase III clinical trial, which opened to accrual in March 2005, will compare whole breast irradiation to partial breast irradiation options (high-dose rate multicatheter brachytherapy, MammoSite balloon catheter, and 3D conformal external beam radiotherapy) with respect to locoregional control, disease-free survival, distant-disease-free survival, overall survival, and quality of life issues.³⁴ Target accrual is 3,000 patients with early-stage (I/II) breast cancer, including patients with node-negative and node-positive (one to three nodes) disease.

Conclusion

While we have not been able to eliminate breast cancer, women today can take advantage of many advances in its detection, diagnosis, treatment, and follow-up care. Diagnoses are made earlier, and treatments for early-stage disease, while still efficacious, are becoming less invasive, thus improving quality of life as well as survival. There are evolving, exciting options in surgery and radiotherapy, and we encourage all practitioners to be aware of and share this exciting information with patients, friends, and family.

REFERENCES

	1.	American Cancer Society. Cancer Facts and Figures 2004 and 2005. Atlanta, Ga: American Cancer Society; 2004 and 2005.
	2.	Ries L, Elsner M, Kosary C, et al, eds. SEER cancer statistics review, 1975-2000. Bethesda, Md: National Cancer Institute.
	3.	Smith R, Saslow D, Sawyer K, et al, eds. American Cancer Society guidelines for breast cancer screening: update 2003. CA Cancer J Clin. 2003;53(3):141-169.
	4.	National Cancer Institute statement on mammography screening. February 21, 2002 Update. Available at: http://www.cancer.gov/newscenter/mammstatement31jan02. Accessed August 28, 2005.
	5.	Effects of radiotherapy and surgery in early breast cancer: an overview of the randomized trials. Early Breast Cancer Trialists’ Collaborative Group. N Engl J Med. 1995;333(22):1444-1455.
	6.	Fisher B, Anderson S, Bryant J, et al. Twenty-year follow-up of a randomized trial comparing total mastectomy, lumpectomy, and lumpectomy plus irradiation for the treatment of invasive breast cancer. N Engl J Med. 2002;347(16):1233-1241.
	7.	Treatment of early-stage breast cancer. NIH consensus statement. June 18-21, 1990;8(6):1-19.
	8.	Fisher B, Dignam J, Wolmark N, et al. Lumpectomy and radiation therapy for the treatment of intraductal breast cancer: findings from National Surgical Adjuvant Breast and Bowel Project B-17. J Clin Oncol. 1998;16(2):441-452.
	9.	Julien JP, Bijker N, Fentiman IS, et al. Radiotherapy in breast-conserving treatment for ductal carcinoma in situ: first results of the EORTC randomized phase III trial 10853. Lancet. 2000;355:528-533.
	10.	Fisher B, Dignam J, Wolmark N, et al. Tamoxifen in treatment of intraductal breast cancer: National Surgical Adjuvant Breast and Bowel Project B-24 randomised controlled trial. Lancet. 1999;353:1993-2000.
	11.	Fisher B, Bryant J, Dignam JJ, et al. Tamoxifen, radiation therapy, or both for prevention of ipsilateral breast tumor recurrence after lumpectomy in women with invasive breast cancers of one centimeter or less. J Clin Oncol. 2002;20(20):4141-4149.
	12.	Fyles A, McCready D, Manchul L, et al. Tamoxifen with or without breast irradiation in women 50 years of age or older with early breast cancer. N Engl J Med. 2004;351(10):963-970.
	13.	McCormick B, Radiation Therapy Oncology Group. Ongoing Phase III randomized study of whole breast radiotherapy versus observation with or without optional tamoxifen in women with good-risk ductal carcinoma in situ of the breast, RTOG-9804. Clinical trial. Ongoing.

	14.	Hughes K, Schnaper L, Berry D, et al. Lumpectomy plus tamoxifen with or without irradiation in women 70 years of age or older with early breast cancer. N Engl J Med. 2004;351(10):971-977.
	15.	Krag D, Weaver D, Ashikaga T, et al. The sentinel node in breast cancer—a multicenter validation study. N Engl J Med. 1998;339(14):941-946.
	16.	Veronesi U, Paganelli G, Viale G, et al. A randomized comparison of sentinel-node biopsy with routine axillary dissection in breast cancer. N Engl J Med. 2003;349(6):546-553.
	17.	Krag D, National Surgical Adjuvant Breast and Bowel Project. Phase III clinical trial to compare sentinel node resection to conventional axillary dissection in clinically node-negative breast cancer patients, NSABP B-32. Clinical trial. Ongoing.
	18.	Giuliano A, American College of Surgeons-Oncology Group. Phase III randomized study of axillary lymph node dissection in women with stage I or IIA breast cancer who have a positive sentinel node, ACOS-OG Z-11. Clinical trial. Ongoing.
	19.	Voogd A, Nielsen M, Petersen J, et al. Differences in risk factors for local and distant recurrence after breast-conserving therapy or mastectomy for stage I and II breast cancer: pooled results of two large European randomized trials. J Clin Oncol. 2001;19(6):1688-1697.
	20.	Veronesi U, Marubini E, Del Vecchio M, et al. Local recurrences and distant metastases after conservative breast cancer treatments: partly independent events. J Natl Cancer Inst. 1995;87:19-27.
	21.	Meek A. Breast radiotherapy and lymphedema. Cancer. 1998;83(12 suppl American):2788-2797.
	22.	Larson D, Weinstein M, Goldberg I, et al. Edema of the arm as a function of the extent of axillary surgery in patients with stage I-II carcinoma of the breast treated with primary radiotherapy. J Radiat Oncol Biol Phys. 1986;12(9):1575-1582.
	23.	Buchholz MF, Mirza NQ, Vlastos G, et al. Long-term complications associated with breast-conservation surgery and radiotherapy. Ann Surg Oncol. 2002;9(6):543-549.
	24.	Storm HH, Andersson M, Boice JD Jr, et al. Adjuvant radiotherapy and risk of contralateral breast cancer. J Natl Cancer Inst. 1992;84(16):1245-1250.
	25.	Locker G, Sainsbury JR, Cuzick J. Breast surgery in the ‘Arimidex, Tamoxifen alone or in combination’ (ATAC) trial: American women are more likely than women from the United Kingdom to undergo mastectomy. Cancer. 2004;101(4):735-740.
	26.	Nattinger A, Kneusel R, Hoffman R, et al. Relationship of distance from a radiotherapy facility and initial breast cancer treatment. J Natl Cancer Inst. 2001;95(17):1344-1346.
	27.	Vicini FA, Kestin L, Chen P, et al. Limited-field radiation therapy in the management of early-stage breast cancer. J Natl Cancer Inst. 2003;95(16):1205-1210.
	28.	Arthur DW, Vicini FA, Kuske RR, et al. Accelerated partial breast irradiation: an updated report from the American Brachytherapy Society. Brachytherapy. 2002;1(4):184-190.
	29.	Kuske RR, Winter K, Arthur DW, et al. A phase II trial of brachytherapy alone following lumpectomy for stage I or II breast cancer: initial outcomes of RTOG 9517. J Clin Oncol. 2004; 22(14S):565.
	30.	King TA, Bolton JS, Kuske RR, et al. Long-term results of wide-field brachytherapy as the sole method of radiation therapy after segmental mastectomy for T (is,1,2) breast cancer. Am J Surg. 2000;180(4):299-304.
	31.	Keisch M, Vicini F, Kuske R, et al. Thirty month results with the MammoSite breast brachytherapy applicator: cosmesis, toxity and local control in partial breast irradiation. Presented at the ASTRO 46th annual meeting 2004.
	32.	Board of Directors, The American Society of Breast Surgeons. Consensus Statement for Accelerated Partial Breast Irradiation. Columbia, Md: The American Society of Breast Surgeons; April 30, 2003.
	33.	Kambiz D, Snider H, Gittleman M, et al. Early experience with balloon brachytherapy for breast cancer. Arch Surg. 2004;139:603-608.
	34.	Vicini F, National Surgical Adjuvant Breast and Bowel Project. A randomized Phase III study of conventional whole breast irradiation (WBI) versus partial breast irradiation (PBI) for women with stage 0, I or II breast cancer, NSABP B-39/RTOG 0413. Clinical Trial. Ongoing.