Breast Abscess Mimicking Malignancy on FDG PET/CT in a Patient with Follicular Lymphoma Undergoing Chemotherapy

A 43-year-old woman diagnosed with follicular lymphoma through biopsy was referred for a baseline fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) scan. The maximum intensity projection images [Figure 1] [Figure 1a] revealed multiple FDG-avid lymph nodes above and below the diaphragm and an intensely hypermetabolic lesion in the epigastric region. Axial fused and corresponding CT images confirmed an FDG-avid left supraclavicular node [Figure 1b] and identified a large metabolically active gastric mass [Figure 1c and d].

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Figure 1:

Baseline positron emission tomography/computed tomography (PET/CT) images reveal (a) multiple fluorodeoxyglucose (FDG)-avid foci above and below the diaphragm and a hypermetabolic focus in the epigastric region. (b) Axial fused PET/CT image shows FDG uptake in the left supraclavicular lymph node (arrow). (c, d) Corresponding CT and fused PET/CT images demonstrate a metabolically active gastric mass (arrow). (e) Follow-up PET/CT aft er six chemotherapy cycles demonstrates complete metabolic resolution of all previously involved sites. (f, g) New findings include a metabolically active, necrotic lesion in the right breast with associated inflammation and effacement of the overlying cutaneous fat planes (arrow). (h) Corresponding right breast ultrasound confirms a complex fluid collection consistent with an abscess.

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The patient underwent six cycles of bendamustine and rituximab (BR) combination chemotherapy. During the treatment, she reported the onset of painful swelling in her right breast. She completed the planned six cycles of chemotherapy, and a posttreatment PET/CT scan, scheduled to evaluate her lymphoma response, was conducted 1 month aft er the final cycle. No interim PET/CT was performed. The results showed complete metabolic resolution of all previously identified lymphomatous lesions [Figure 1e and h]. However, a new FDG-avid lesion was found in the right breast [Figure 1f], which exhibited necrotic changes with inflammatory changes and loss of fat planes involving the overlying skin [Figure 1g].

Considering the complete response of the known disease along with the appearance of this new necrotic hypermetabolic lesion, possible diagnoses included infection, secondary lymphoma involvement, or a new primary breast malignancy. An ultrasound of the breast indicated the presence of a fluid collection suggestive of an abscess. Laboratory investigations demonstrated leukocytosis (13.2 × 109/L, 82% neutrophils) and an elevated C-reactive protein (CRP) level (42 mg/L), findings indicative of an active infection. These results, along with preexisting BR-induced lymphopenia (0.6 × 109/L), align with the patient’s immunocompromised state. The patient subsequently underwent incision and drainage. Histopathological analysis of the aspirate confirmed necrotizing inflammation consistent with an abscess and showed no evidence of malignancy.

This case illustrates a significant diagnostic challenge in an immunocompromised patient with follicular lymphoma undergoing chemotherapy, who developed a breast abscess that mimicked malignancy on FDG PET/CT. Although PET/CT is an essential modality for staging and response assessment in lymphomas, including follicular lymphoma,^[1-3] it is susceptible to false-positive findings due to inflammatory or infectious processes.^[4,5] Immunosuppression from chemotherapy, particularly regimens such as bendamustine-rituximab, increases the risk of infections, which can show intense FDG uptake and mimic neoplastic lesions.^[6] Distinguishing infection from malignancy on imaging alone can be challenging without corroborative clinical signs. This case underscores the importance of correlating PET/CT findings with clinical assessment, adjunctive imaging, and, when indicated, histopathological confirmation to avoid misinterpretation and inappropriate management.^[7,8] Furthermore, correlation with laboratory parameters such as a complete blood count, erythrocyte sedimentation rate, and CRP can provide crucial evidence supporting an infectious or inflammatory etiology.