Case number:	103
Age:	82
Clinical presentation:	Postmenopausal woman had undergone microdochectomy for right nipple discharge. Histopathology of the excised duct showed benign papilloma. On follow-up a year later, she presented with a left breast lump. Mammography and breast ultrasound dated 2015 reveal a new lesion in the left breast. Compared with a previous mammogram dated 2014, follow-up reveals developing asymmetry in the left breast. Interval change is seen. Diagnosed as highly suspicious for malignancy, BI-RADS 4C on imaging, as mucinous carcinoma on cytology, and as mucinous carcinoma, pT2N0 on histopathology.

Mammography:

Breast composition:	ACR category b (there are scattered areas of fibroglandular density)
Mammography features:

‣ Location of the lesion:	September 2014: Left breast, upper outer quadrant at 1–3 o’clock, middle third
‣ Mass:
• Number:	Multiple
• Size:	Largest 0.4 cm
• Shape:	Round
• Margins:	Circumscribed
• Density:	Equal
‣ 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:	Multiple simple cysts

Breast composition:	ACR category b (there are scattered areas of fibroglandular density)
Mammography features:

‣ Location of the lesion:	July 2015: Left breast, upper outer quadrant at 2 o’clock, posterior third
‣ Mass:
• Number:	Multiple
• Size:	Largest 1.7 × 1.0 cm (this is the developing asymmetry)
• Shape:	Oval
• Margins:	Indistinct posterior margin
• 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: July 2015: Left breast, upper outer quadrant at 2 o’clock

‣ Mass
• Location:	July 2015: Left breast, upper outer quadrant at 2 o’clock
• Number:	1
• Size:	2.0 × 1.0 cm (this is the developing asymmetry)
• Shape:	Irregular
• Orientation:	Not parallel
• Margins:	Partly circumscribed and partly indistinct margins
• Echo pattern:	Heteroechoic
• Posterior features:	No posterior features
‣ Calcifications:	None
‣ Associated features:	None
‣ Special cases:	None

BI-RADS:

BI-RADS Category (2014): 2 (benign)
BI-RADS Category (2015): 4C (high suspicion for malignancy)

Further assessment:

Further assessment advised: Referral for cytology

Cytology:

Cytology features:

‣ Type of sample:	FNAC
‣ Site of biopsy:
• Laterality:	Left
• Quadrant:	Upper outer
• Localization technique:	Palpation
• Nature of aspirate:	0.2 mL of mucoid material
‣ Cytological description:	Numerous moderately cohesive clusters and balls of malignant cells dispersed in a mucinous background
‣ Reporting category:	Malignant
‣ Diagnosis:	Mucinous carcinoma
‣ Comments:	None

Histopathology:

MRM

Histopathology features:

‣ Specimen type:	MRM
‣ Laterality:	Left
‣ Macroscopy:	Specimen (28.0 × 13.0 × 6.0 cm) with an overlying skin flap (11.0 × 5.0 cm). The nipple and areola are unremarkable. On serial sectioning, a small well-circumscribed area (2.1 × 1.3 × 1.0 cm) is identified in the upper outer quadrant, 5.0 cm from the skin and 1.5 cm from the base. Cut surface shows mucoid areas. The remaining breast tissue is unremarkable
‣ Histological type:	Mucinous carcinoma
‣ Histological grade:	Grade 2 (2 + 2 + 1 = 5)
‣ Mitosis:	4
‣ Maximum invasive tumour size:	2.1 cm in greatest dimension
‣ Lymph node status:	0/22
‣ Peritumoural lymphovascular invasion:	Absent
‣ DCIS/EIC:	Absent
‣ Margins:	Free of tumour
‣ Pathological stage:	pT2N0
‣ Biomarkers:
‣ Comments:

Case summary:

Postmenopausal woman had undergone microdochectomy for right nipple discharge, histopathology of the excised duct showed benign papilloma. On follow up a year later, she presented with left breast lump. Mammography and breast ultrasound dated 2015 reveal new lesion in left breast. Compared to previous mammogram dated 2014, follow-up reveals developing asymmetry in left breast. Interval change is seen, diagnosed as highly suspicious of malignancy, BI-RADS category 4C on imaging, mucinous carcinoma on cytology and Mucinous carcinoma, pT2N0 on histopathology.

Learning points:

Mucinous carcinoma incidence is higher in women older than 75 years (7%), compared with women younger than 35 years of age (1%). Grossly, it is well-circumscribed, fluctuant to palpation, and formed by a gelatinous mass held together by delicate septa. Mucinous carcinomas are divided into type A (a paucicellular type without neuroendocrine differentiation) and type B (a hypercellular type with neuroendocrine differentiation). There appears to be no influence of this separation on survival.