Case number:	066
Age:	58
Clinical presentation:	Postmenopausal woman with average risk of developing breast cancer presented with a lump in the right breast noticed on breast self-examination.

Mammography:

Breast composition:	ACR category a (the breasts are almost entirely fatty)
Mammography features:

‣ Location of the lesion:	Right breast, lower inner quadrant at 5 o’clock, anterior third
‣ Mass:
• Number:	1
• Size:	1.8 × 1.5 cm
• Shape:	Oval
• Margins:	Partly circumscribed and partly indistinct
• Density:	High
‣ Calcifications:
• Typically benign:	None
• Suspicious:	None
• Distribution:	None
‣ Architectural distortion:	None
‣ Asymmetry:	None
‣ Intramammary node:	None
‣ Skin lesion:	None
‣ Solitary dilated duct:	None
‣ Associated features:	None

Ultrasound:

Ultrasound features: Right breast, lower inner quadrant 5 o’clock position

‣ Mass
• Location:	Right breast, lower inner quadrant 5 o’clock position
• Number:	1
• Size:	2.0 × 1.2 cm
• Shape:	Irregular
• Orientation:	Parallel
• Margins:	Partly circumscribed and partly indistinct margins
• Echo pattern:	Isoechoic
• Posterior features:	No posterior features
‣ Calcifications:	None
‣ Associated features:	Internal vascularity
‣ Special cases:	None

BI-RADS:

BI-RADS Category: 4B (moderate suspicion of malignancy)

Further assessment:

Further assessment advised: Referral for cytology

Cytology:

Cytology features:

‣ Type of sample:	FNAC (solid lesion)
‣ Site of biopsy:
• Laterality:	Right
• Quadrant:	Lower inner
• Localization technique:	Palpation
• Nature of aspirate:	Very transparent sticky material aspirated
‣ Cytological description:	Smears show loosely cohesive and many single isolated malignant cells with round nuclei. The background shows mucinous material. Branching capillary structures are also seen
‣ Reporting category:	Malignant
‣ Diagnosis:	Mucinous carcinoma
‣ Comments:	Pitfalls: The appearance of malignant cells in colloid carcinoma is often low grade, requiring careful exclusion of other benign entities with mucinous features, such as mucocele and fibroadenoma with abundant mucinous stroma

Histopathology:

Breast-conserving surgery

Histopathology features:

‣ Specimen type:	Breast-conserving surgery
‣ Laterality:	Right
‣ Macroscopy:	Cut surface shows an irregular tumour (1.5 × 1.5 × 1.2 cm) with glistening gelatinous areas, soft in consistency
‣ Histological type:	Mucinous carcinoma
‣ Histological grade:	Grade 1 (2 + 2 + 1 = 5)
‣ Mitosis:	5
‣ Maximum invasive tumour size:	1.7 cm in greatest dimension
‣ Lymph node status:	0/30
‣ Peritumoural lymphovascular invasion:	Present
‣ DCIS/EIC:	Not identified
‣ Margins:	Free of tumour
‣ Pathological stage:	pT1cN0
‣ Biomarkers:
‣ Comments:

Case summary:

Postmenopausal woman presented with lump in the right breast. Diagnosed as right breast mass of suspicious morphology, BI-RADS 4B on imaging, as mucinous carcinoma on cytology, and as mucinous carcinoma, pT1cN0 on histopathology.

Learning points:

Mucinous carcinoma is also known as colloid carcinoma, gelatinous carcinoma, or mucous carcinoma. This subtype of invasive breast carcinoma is seen in 3% of all breast cancers with malignant cells seen in lakes of mucin. The malignant cells in colloid carcinoma are often low grade. Benign breast lesions such as mucocele and fibroadenoma with abundant mucinous stroma and mucinous features need to be considered as differential diagnoses and should be excluded.