Comparison of 18F-FDG PET/CT for Systemic Staging of Newly Diagnosed Invasive Lobular Carcinoma Versus Invasive Ductal Carcinoma

Abstract

Although guidelines such as those of the National Comprehensive Cancer Network consider (18)F-FDG PET/CT for systemic staging of newly diagnosed stage III breast cancer patients, factors in addition to stage may influence the utility of PET/CT. Because invasive lobular carcinoma (ILC) is less conspicuous than invasive ductal carcinoma (IDC) on (18)F-FDG PET, we hypothesized that tumor histology may be one such factor. We evaluated PET/CT systemic staging of patients newly diagnosed with ILC compared with IDC.

Methods: In this Institutional Review Board-approved retrospective study, our Hospital Information System was screened for ILC patients who underwent PET/CT in 2006-2013 before systemic or radiation therapy. Initial stage was determined from examination, mammography, ultrasound, MR, or surgery. PET/CT was performed to identify unsuspected distant metastases. A sequential cohort of stage III IDC patients was evaluated for comparison. Upstaging rates were compared using the Pearson χ(2) test.

Results: The study criteria were fulfilled by 146 ILC patients. PET/CT revealed unsuspected distant metastases in 12 (8%): 0 of 8 with initial stage I, 2 of 50 (4%) stage II, and 10 of 88 (11%) stage III. Upstaging to IV by PET/CT was confirmed by biopsy in all cases. Three of 12 upstaged patients were upstaged only by the CT component of the PET/CT, as the metastases were not (18)F-FDG-avid. In the comparison stage III IDC cohort, 22% (20/89) of patients were upstaged to IV by PET/CT. All 20 demonstrated (18)F-FDG-avid metastases. The relative risk of PET/CT revealing unsuspected distant metastases in stage III IDC patients was 1.98 times (95% confidence interval, 0.98-3.98) that of stage III ILC patients (P = 0.049). For (18)F-FDG-avid metastases, the relative risk of PET/CT revealing unsuspected (18)F-FDG-avid distant metastases in stage III IDC patients was 2.82 times (95% confidence interval, 1.26-6.34) that of stage III ILC patients (P = 0.007).

Conclusion: (18)F-FDG PET/CT was more likely to reveal unsuspected distant metastases in stage III IDC patients than in stage III ILC patients. In addition, some ILC patients were upstaged by non-(18)F-FDG-avid lesions visible only on the CT images. Overall, the impact of PET/CT on systemic staging may be lower for ILC patients than for IDC patients.

Keywords: 18F-FDG; PET/CT; breast cancer; ductal; lobular; staging.

FIGURE 1

A 62-y-old woman with initial stage III ILC upstaged to IV by ¹⁸F-FDG PET and CT. (A) Axial fused ¹⁸F-FDG PET/CT image demonstrates previously unknown right humeral head metastases as ¹⁸F-FDG–avid osseous lesion (arrow). (B) Metastatic lesion is apparent as sclerotic osseous lesion on CT (arrow). Biopsy confirmed osseous metastasis.

FIGURE 2

A 56-y-old woman with initial stage III ILC upstaged to IV on CT component of ¹⁸F-FDG PET/CT. (A) Axial ¹⁸F-FDG PET does not demonstrate suggestive foci. (B) Axial CT component of PET/CT demonstrates multiple osseous sclerotic lesions suggestive of metastases (arrow). (C) Axial fused ¹⁸F-FDG PET/CT image confirms that osseous sclerotic lesions demonstrate background ¹⁸F-FDG avidity. Biopsy confirmed osseous metastasis.

FIGURE 3

A 52-y-old woman with initial stage III left breast ILC upstaged to IV by ¹⁸F-FDG PET and CT. (A) Axial fused ¹⁸F-FDG PET/CT image demonstrates previously known ipsilateral left axillary nodal metastasis as ¹⁸F-FDG–avid lesion (solid arrow), as well as previously unknown contralateral right axillary node (dashed arrow). (B) Both ipsilateral and contralateral axillary nodal lesions are apparent as enlarged and rounded nodes on CT. Biopsy of contralateral right axillary node demonstrated nodal metastasis. Contralateral axillary nodal metastases are distant metastases (M1 disease) as classified by American Joint Committee on Cancer (18).

FIGURE 4

A 64-y-old woman with initial stage III ILC false-positive for distant metastasis on ¹⁸F-FDG PET/CT. (A) Axial ¹⁸F-FDG PET demonstrates ¹⁸F-FDG–avid (SUV, 2.9) focus in left abdomen (arrow). (B) Axial CT component of PET/CT demonstrates 2.1-cm adrenal nodule with average Hounsfield units of 29 (arrow). Biopsy resulted in diagnosis of benign adrenal adenoma.

FIGURE 5

A 42-y-old woman with initial stage III IDC upstaged to IV by ¹⁸F-FDG PET. (A) Axial fused ¹⁸F-FDG PET/CT image demonstrates previously unknown right ilium metastases as ¹⁸F-FDG–avid osseous lesion (arrow). (B) No definite corresponding lesion is seen on axial CT component of PET/CT. (C) Axial fused ¹⁸F-FDG PET/CT image confirms osseous localization of ¹⁸F-FDG–avid focus (arrow). (D) No corresponding focus is seen on ^99mTc-MDP bone scan (anterior [left] and posterior [right] spot views of pelvis shown). Biopsy confirmed osseous metastasis.

FIGURE 6

A 46-y-old woman with initial stage III IDC false-positive for distant metastasis on CT component of ¹⁸F-FDG PET/CT. (A) Axial ¹⁸F-FDG PET does not demonstrate suggestive foci. (B) Axial CT component of PET/CT demonstrates osseous sclerotic lesion (arrow) in T1 vertebra. (C) Axial fused ¹⁸F-FDG PET/CT image confirms that osseous sclerotic lesion (arrow) demonstrates background ¹⁸F-FDG avidity. Biopsy of sclerotic lesion yielded dense cortical bone without evidence of malignancy, consistent with bone island.