道下 由紀子¹, 森島 勇², 小沢 昌慶³, 内田 温³, 大河内 良美⁴, 石黒 和也⁴, 菊地 和徳³

Yukiko MICHISHITA¹, Isamu MORISHIMA², Masayoshi OZAWA³, Atsushi UCHIDA³, Yoshimi OKOUCHI⁴, Kazuya ISHIGURO⁴, Kazunori KIKUCHI³

¹聖マリアンナ医科大学放射線医学講座, ²筑波メディカルセンター病院乳腺科, ³筑波メディカルセンター病院病理科, ⁴筑波メディカルセンター病院臨床検査科

¹Department of Radiology, St. Marianna University School of Medicine, ²Department of Senology, Tsukuba Medical Center Hospital, ³Department of Pathology, Tsukuba Medical Center Hospital, ⁴Department of Clinical Laboratory, Tsukuba Medical Center Hospital

キーワード : breast cancer, breast ultrasound, intraductal papilloma, internal echo change, doubling time

乳癌の腫瘍倍加時間は平均4ヵ月とされる．今回，2年3ヵ月の経過で明らかな腫瘤径増大はなく，内部エコーの変化が契機となり浸潤性乳癌と診断された1例を経験した．症例は40代女性，乳癌検診で初めて左乳房2時方向に縦横比の大きな分葉形高エコー腫瘤を指摘された．後方エコーは増強，カラードプラで腫瘤辺縁に血流信号を認め，エラストグラフィではTsukuba elasticity score 4，fat lesion ratio 14.58と歪みの低下があり，粘液癌や乳管内乳頭腫（intraductal papilloma：IDP）等の可能性を考えた．穿刺吸引細胞診（fine needle aspiration cytology：FNAC）で粘液は吸引されず，IDPや線維腺腫（乳腺症型）が推定された．超音波（ultrasonography：US）と細胞診の所見に解離はなく，IDP疑いとして経過観察の方針となった．FNACから7ヵ月後のUSでは大きな変化なく，1年1ヵ月後のUSで腫瘤辺縁の低エコー部は厚みを増した印象があったが腫瘤径の増大はなかった．2年3ヵ月後のUSでは腫瘤辺縁の低エコー部がさらに増し，腫瘤全体の内部エコーレベルも低下した．この時点で針生検を施行し，浸潤性乳管癌の診断を得て初期治療を行った．US画像で変化を呈した部分について病理組織標本を照らし合わせてみると，小腺管や膠原線維の増生が顕著で，内部エコーレベル低下の要因と考えられた．一般に，経過観察中の画像評価では腫瘍増大の有無に焦点が当てられるが，腫瘍倍化時間の長い乳癌も存在する．USで経過を追う際には，内部エコーレベルの変化にも留意する必要がある．

We were able to observe a case of invasive breast cancer diagnosed based on internal echo changes without an obvious increase in tumor size for 2 years and 3 months. Generally, breast cancer doubling time is considered to be 4 months on average. In this case, the tumor itself had not grown, but the internal echoes revealed some changes during the time period. A medical checkup revealed a left breast mass in a woman in her 40s. On ultrasonography (US), it had a lobulated shape, a well-defined border, a hyperechoic pattern with posterior echo enhancement, and a large depth-width ratio. Color Doppler US showed a blood flow signal at the edge of the mass, and elastography showed decreased strain. US indicated a mucinous carcinoma or intraductal papillary lesion. US-guided fine-needle aspiration cytology (FNAC) showed no mucus aspiration, suggesting intraductal papilloma(IDP) or fibroadenoma (mastopathic type). There was no discrepancy between the US and cytology findings, and the patient was placed on follow-up observation for suspected IDP. Thirteen months after FNAC, the tumor had not increased in volume, but the hypoechoic rim of the tumor became slightly clearer. Twenty-seven months after FNAC, the tumor had not grown, but the internal echo level had decreased. Breast cancer was suspected, and the diagnosis was confirmed by core-needle biopsy. The histopathological specimen was compared with the part showing the change on the US image. There were parts where the small mammary ducts were rich with cancer cells and the collagen fiber had increased. It was speculated that these changes were the factors that decreased the internal echoes. Generally, follow-up evaluation of images focuses on tumor growth, but there are also breast cancers with long tumor doubling times. We would like to emphasize the great importance that should be placed upon the internal echo changes of tumors.