Background reading

The breast is an organ whose structure reflects its special function: the production of milk for lactation (breast feeding). The epithelial component of the tissue consists of lobules, where milk is made, which connect to ducts that lead out to the nipple. Most cancers of the breast arise from the cells which form the lobules and terminal ducts. These lobules and ducts are spread throughout the background fibrous tissue and adipose tissue (fat) that make up the majority of the breast. The male breast structure is nearly identical to the female breast, except that the male breast tissue lacks the specialised lobules, since there is no physiologic need for milk production by males.

The type of breast cancer is determined on which cells in the breast are being affected and it can also refer to whether the cancer has spread or not (in situ or invasive).

Ductal carcinoma is the most common type of breast cancer and starts in the milk ducts.

Lobular carcinoma is the second most common type of breast cancer and starts in the cells that line the lobules.

PET-CT is not part of the current recommendations for initial staging in breast cancer patients however there is mounting evidence that in high risk patients

the results of this examination can modify staging and management of the disease.

Patient history

A 59 year old patient with HER positive left breast cancer. CT scan suggested neck and mediastinum node involvement. Patient had 21 cycles of neoadjuvant chemotherapy as node involvement was not known.

ARSAC Practitioner authorisation 

¹⁸F-FDG PET-CT – base of skull to proximal third of femur. 

Injected activity

Patient weight was 111kg and the injected activity was 394MBq (range 349.7 to 400MBq). 

Pre-injection blood sugar levels

Patient completed seven and half hour fast (plain water only) prior to 18F-FDG administration. Patient is not diabetic. Pre-injection blood sugar level was recorded as 5.2mmol/L. 

Uptake time

Uptake time was 66 minutes.

Clinical indication for PET-CT 

Assessment of the neck and mediastinum nodes for disease involvement and re-stating of breast cancer. 

Diagnostic Reference Level for F18 FDG 

3.5MBq per kilogram of weight. Minimum activity 100MBq and maximum 400MBq ± 10%.

Scan protocol

Patient was positioned supine with both arms by side of torso. The scan area was skull base to proximal third of femur in a craniocaudal direction.

CT mA: Smart

CT kVp: 120kV

CTDI: 5.36 mGy

DLP: 452.25mGy.cm

Number of PET beds: 9

Time per PET bed: 2 minutes

Scan Findings

The known left breast malignancy [1] is intensely avid. Multiple avid left axillary lymph nodes [2]. 

Avid left subpectoral lymph nodes. Avid left supraclavicular and superior mediastinal lymph nodes [3]. Several intensely avid left internal mammary lymph nodes [4]. 

Intense tracer uptake mapping onto a nodule within the left lobe of thyroid. Ultrasound +/- FNA suggested. 

Tiny 4 mm subpleural nodule in the left lower lobe does not show any tracer uptake above that of background lung parenchyma. This is likely to be benign, but the small size may make it beyond the resolution of FDG PET-CT and monitoring on follow-up imaging is advised. No FDG avid lung lesion. 

Gallstone within the gallbladder. No biliary dilatation. 

15 mm left adrenal nodule measuring 20 Hounsfield units does not show increased tracer uptake. This is likely to represent an adrenal adenoma. Colonic diverticulosis. The sigmoid colon there is an area of intense tracer uptake [5] which maps onto an area of apparent intraluminal soft tissue. Appearances are concerning for a sigmoid polyp or small cancer. Further small foci of intense tracer uptake in the sigmoid colon and descending colon may represent areas of focal inflammation or neoplasia, colonoscopy advised. 

Bilateral symmetrical uptake within the shoulder joints consistent with degenerative change. No suspicious bone lesions. 

Reference values: Mediastinal (ascending aorta) blood pool sample max SUV = 3.3 g/ml Liver sample max SUV = 4.4 g/ml

Impressions

Intensely avid left breast mass with associated left axillary, left subpectoral, left supraclavicular, left superior mediastinal, and left internal mammary lymphadenopathy. 

4 mm subpleural nodule in the left lower lobe of the lung does not demonstrate increased tracer uptake. This is likely to be benign, but the small size may make it beyond the resolution of FDG PET-CT and monitoring on follow-up imaging is advised. 

Intense tracer uptake mapping onto a nodule within the left lobe of thyroid. Ultrasound +/-FNA suggested. 

Possible polyp in the sigmoid colon with further areas of indeterminate focal uptake elsewhere in the colon. Colonoscopy advised.