Lipoma: A benign tumor composed of fat tissue, which can grow in the supraclavicular fossa, presenting as a soft, non-tender mass. This diagnosis is likely due to the common occurrence of lipomas in various parts of the body, including the neck region.

Hematoma or seroma: Fluid collections that can occur in the soft tissues of the supraclavicular fossa, possibly due to trauma or surgical procedures. These conditions can present as soft, non-lymph node enlargements.
Soft tissue abscess: An infection of the soft tissues that can cause swelling and may feel soft due to the presence of pus, although it is typically accompanied by signs of infection such as redness, warmth, and tenderness.
Cystic hygroma: A congenital condition that can present as a soft, cystic mass in the neck, including the supraclavicular area, although it is more commonly diagnosed in infancy.

Metastatic disease: Although less likely, it is crucial not to miss the possibility of metastasis to the supraclavicular lymph nodes from various cancers, such as lung, breast, or abdominal malignancies. The presence of a hard, fixed mass would be more suggestive, but soft masses should not entirely rule out this possibility without further investigation.
Thyroid mass: An enlarged thyroid gland or a thyroid nodule can sometimes extend into the supraclavicular fossa, presenting as a soft mass. Given the potential for thyroid cancer, this diagnosis should not be overlooked.

Neurofibroma: A benign nerve sheath tumor that can occur in the supraclavicular fossa, presenting as a soft mass. It is associated with neurofibromatosis type 1 (NF1) but can also occur sporadically.
Branchial cleft cyst: A congenital anomaly that can present as a soft, cystic mass in the neck, including the supraclavicular area, although it is more commonly found in the lateral neck.
Madelung's disease (Multiple Symmetric Lipomatosis): A rare condition characterized by the growth of multiple lipomas in a symmetric pattern, which can include the supraclavicular fossa.