Pectoralis Major Muscle Flap With Fat Grafting in Oncoplastic Breast-Conserving Surgery.

CASE PRESENTATION
A 52-year-old woman (height 152.1 cm, weight 57.0 kg, body mass index 24.6 kg/m2) was diagnosed with breast cancer (cT2N0M0) in the upper outer quadrant of the left breast. She had moderately sized breasts without ptosis (Fig. 1). The tumor measured 33 mm on magnetic resonance imaging. Although the patient desired breast conservation, simple excision with direct closure was deemed inadequate for cosmetic preservation. Therefore, the PMFG procedure was planned.
A lateral approach was used for partial mastectomy, excising a cylindrical segment (65 mm in diameter, 25 mm in height; resected weight: 65 g, volume: 70 mL). (See figure, Supplemental Digital Content 1, which displays resected breast cancer specimens. The cylindrical specimen measured 65 mm in diameter and 25 mm in height, with a resected weight of 65 g and a volume of 70 mL, https://links.lww.com/PRSGO/E791.) Through the same incision, dissection was performed above the PM, including the retromammary fat layer, followed by subpectoral dissection (Fig. 2). The costal origin of the PM muscle was transected laterally to medially, and the sternal origin was transected caudally to cranially, preserving the internal mammary perforators. While preserving the thoracoacromial vessels, the medial portion of the clavicular origin was released, and the PM muscle flap was elevated. (See figure, Supplemental Digital Content 2, which displays the schematic illustration of PMFG. The PM muscle flap was elevated over the thoracoacromial vessels while preserving the internal mammary perforators along the sternal border. FG was then performed into the muscle flap, https://links.lww.com/PRSGO/E792.) Preoperative computed tomography estimated a PM flap volume of 80 mL.
Subsequently, liposuction was performed on the inner thighs, and 150 mL of purified fat was injected into the PM muscle, fascia, and retromammary layer (Fig. 3). The PMFG was used to fill the defect, and the breast shape was assessed in the seated position. Two closed-suction drains were inserted. (See Video [online], which provides an overview of the surgical procedure.)
The postoperative course was uneventful. The 2 drains were removed, and the patient was discharged on postoperative day 6. Pathology confirmed negative margins. Six months after surgery (3 mo after the completion of radiotherapy), the cosmetic outcome was excellent (Fig. 4), with no pain or upper limb dysfunction.

DISCUSSION
The PM muscle is located posterior to the mammary gland and receives a rich blood supply from the thoracoacromial, internal mammary, and lateral thoracic vessels. Although the PM muscle flap provides sufficient mobility to cover defects after partial mastectomy, we considered that volume augmentation with FG would be necessary in view of its postoperative atrophy. Intramuscular FG into vascularized muscle flaps, such as the latissimus dorsi and PM, has been reported in several case series, with complication profiles dominated by local events (fat necrosis and infection) and no reported cases of clinical fat embolism when standard safety precautions are followed.4,5
We focused on 4 key aspects when elevating the PM muscle flap:
Access through a single incision: A lateral partial mastectomy allows PM muscle flap elevation through the same incision, avoiding additional scarring, which is a unique advantage not commonly found in other oncoplastic breast–conserving surgery techniques.

Preservation of internal mammary perforators: Internal mammary perforators were preserved by transecting the sternal origin of the PM. This minimized the risk of bleeding but ensured perfusion of the residual breast tissue.

Inclusion of fascia and retromammary fat: This increased the flap volume and provided a vascular scaffold to enhance fat graft survival.

Preservation of thoracoacromial vessels: Although the clavicular origin was transected to improve mobility, the thoracoacromial pedicle was preserved, and perfusion was maintained.

VOLUME CONSIDERATIONS
Postlumpectomy breast volume reportedly decreases by approximately 20% during 5 years owing to radiation therapy.6 Based on this report, we estimated that a reconstruction volume of 90 mL would be necessary for a 70-mL defect created by the current resection. Preoperative computed tomography estimated the PM muscle flap volume to be 80 mL, which was expected to decrease by 50% over time,7 yielding a volume of approximately 40 mL. Therefore, an additional volume of 50 mL was required. Assuming a 50% fat graft take rate,8 at least 100 mL of fat would be needed, and we injected 150 mL to ensure adequacy. The favorable cosmetic outcome in this case may also be attributable, at least in part, to the timing of postoperative radiotherapy. Radiotherapy was initiated 3 months after surgery, with the aim of balancing fat graft survival and oncological safety. A previous study indicated that adjuvant radiotherapy remains oncologically safe if started within 20 weeks postoperatively,9 whereas grafted fat is thought to reach a relatively stable state at approximately 3 months.10 Therefore, radiotherapy was administered at this time. One limitation of this study is that we did not quantitatively evaluate the long-term atrophy rate of the PM muscle flap. Future prospective studies are needed to establish objective data on the temporal changes in flap volume.

COMPARISON WITH OTHER FLAPS
PMFG is suited for upper breast defects in patients with small to moderately sized breasts and minimal thickness. For upper outer quadrant defects, the lateral intercostal artery perforator flap3 and thoracodorsal artery perforator flap4 flaps are well established and provide adequate volume. However, these approaches often leave noticeable scars from the lateral chest to the back and may require intraoperative repositioning. In contrast, PMFG can be performed with the patient in the supine position immediately after tumor resection without additional incisions.
Although the PM muscle flap can be used to address extensive defects due to its mobility, its inherent thinness requires cautious use in large or thick breast reconstructions. Nevertheless, its rich vascularity provides an excellent bed for the FG, allowing for staged volume enhancement through secondary grafting.

CONCLUSIONS
We successfully performed a novel oncoplastic breast–conserving procedure (PMFG) combining the PM muscle flap with FG. This technique requires no additional incisions or patient repositioning and offers excellent maneuverability and cosmetic results.

DISCLOSURE
The authors have no financial interest to declare in relation to the content of this article.

Supplementary Material